What is Two-Factor Authentication (2FA): Everything You Need to Know

In this guide, you’ll learn what 2FA is, how it can protect your business against today’s threats, and the best ways to implement it in your application.

Passwords are dead, and most of your competition has moved on. So if your platform still depends on passwords alone, you’re leaving the door wide open for hackers.

Let’s get right into it.

What is 2FA?

2FA  is a security process that uses two different forms of identification for verification. 

As passwords become more vulnerable, using just one mode of verification won’t secure your users. But introducing a second layer (2FA) makes it more difficult for hackers to compromise your users’ data.

To understand the concept, let’s take the example of the ATM. 

You need to have your card and PIN to withdraw money. Putting in the card will not dispense cash. 

The PIN is also pretty useless without your card. But, in conjunction, they create security for your account.

2FA authentication works the same way. You verify yourself through a second process after entering your password. 

Your password may be simple and can get broken by specialised software. But breaking the second layer will take work (if not impossible in most cases).

What are the different types of authentication?

Here are the different types of user authentication:

• Single-factor authentication
• Two-Factor authentication (2FA)
• Multi-Factor Authentication (MFA)
• Step-Up Authentication
• Risk-Based Authentication (RBA)
• Passwordless authentication
• Adaptive authentication
• Biometric authentication
• Token-based authentication, and
• Out-of-band authentication

Let’s now get into what each type is and how it works for various use cases.

1. Single-Factor Authentication (SFA)

Single-factor authentication, as the name implies, requires that the user only provide one piece of information to verify their identity. It’s the most basic type of authentication and requires just a PIN or password.

An example of one factor in use is a simple login to an app or website, whereby the user simply uses their name and password/PIN.

Many users like one-factor authentication because it allows them to log in to their accounts with just one step. However, of course, it comes with significant security risks. For example, if a hacker can guess the PIN of that user, or is opportuned to see it while the user was logging in previously, they can also log in at any time.

Other methods of finding out these passwords or PINs are through phishing scams, force, or general data breaches on the platform involved. So, without a second layer, it’s just as if you simply closed your door shut behind you without locking it with a key.

That’s why it’s not advisable to use one-factor authentication unless it is for non-sensitive access like news websites or online forums.

Anywhere you store personal, confidential or financial data, you should have at least two-factor authentication in place.

2. Two-Factor Authentication (2FA)

Two-Factor Authentication is different in that a user will be required to provide another piece of information to accompany the password/PIN.

This second layer of protection means anyone logging in must provide an extra proof of identity before gaining access to that account. This proof of ID could be a one-time code sent to the real user via SMS or email, even an in-app approval request.

This means that the person logging in must have access to the linked device or the user’s email/SMS inbox to gain access.

This double-check method reduces the chances of unauthorised access. That’s why it’s a standard security practice for banking, email, social media accounts and others that store sensitive data.

However, many of them still go even further to ask for more proof, as the case may be, which brings us to the next section on MFA.

3. Multi-Factor Authentication (MFA)

MFA refers to any method that requires more than one steps to grant user access. And as you would imagine, it’s safer than 2FA, even if it may be more stressful for the original user each time they log in.

Most times it involves:

1. Something the user knows either by heart or written down somewhere (a password or PIN)
2. Something they have access to (a key or device like a phone, laptop, or flash drive), and
3. Something that’s part of their physical identity (biometric data like a fingerprint, facial scan, or palm proof). 

All in one login.

These multiple steps make it more difficult for attackers. Because even if they manage to access the password, they still need the user’s fingerprint, for example.

This method is highly needed in high-security environments, like health records, enterprise systems, and cloud infrastructure, where breaches can be more disastrous financially or life-threatening.

Yes, the long user login can be frustrating. But the stress is worth it when compared to the damage unauthorised access could cause.

4. Passwordless authentication

Passwordless authentication is a simple login system that doesn’t require passwords.

Users simply input their email, for example, and are asked to verify their identity via other means, such as:

• One-time magic link sent to their email
• Fingerprint scan
• Face recognition check, or
• Push notification sent to a trusted device.

An example of this method is the now-popular and easy-to-use “Login with Email” or “Login with Apple ID” method. Next, you’ll be asked to check and click your email for a link that’s been sent, and you’re in.

With this method, you won’t even need a password or any other information mentioned earlier.

Passwords are weak; going passwordless takes that risk away. At the same time, it is user-friendly and fast. And the good thing is, more companies and apps are going passwordless, as the user experience becomes more paramount,  especially since this method is also highly secure for users.

5. Adaptive authentication

Adaptive authentication can also be called risk-based authentication. Why? This is another innovative and flexible method that adjusts according to the user’s most recent or frequent login experiences.

In an adaptive method, the system notices and recognises where the user is logging in from, for example, the device they’re using, the time they frequently log in, or how they go about the login process.

Here’s an example.

Assuming the user usually logs in from their iPhone between 9 am and 5 pm every day, from their home, and each time, the system only asks for a password.

Then, one random evening, around 1 a.m., the same user tries logging in from a new laptop in a different country. The system notices the change and may ask for additional verification. A fingerprint scan, a security code that will be sent to that phone, etc.

This type of security is dynamic and is mainly powered by Artificial Intelligence (AI).

It lets you enjoy a smooth process and raises the security bar only when the situation feels suspicious.

6. Step-Up Authentication

The Step-Up Authentication uses the logic of letting the user access basic features and flows in the given platform, but will request verification only when they try to perform sensitive actions.

This method means every other method mentioned above (minus one-factor) will be required when trying to perform specific actions on that account. Money transfers, password change, accessing restricted information, change of email or phone number, etc.

This approach makes it easy for the user to gain access easily until it’s time to do more. This practice is widespread among new platforms trying to keep their new user comfortable while still protecting them.

It’s especially popular in banking apps, enterprise platforms, and customer portals that want to keep easy daily use simple while tightening security for critical actions.

Those are the different types of authentication methods. And for the sake of this guide, we’ll be looking deeper into the second type: 2FA. 

How does 2FA work?

With 2FA, you add an extra layer of security to your application. 

Your users don’t get instant access to their accounts after they enter their passwords. 

Instead, they need to provide an extra bit of verification. 

The kind of additional verification they provide is one of these three:

• Knowledge: Something they already know. This includes username-password combination, PIN or CVV number.
• Possession: Something they already own. A cell phone where they receive OTPs or verification codes, a phone app or an ID card will do for this.
• Inherence: Something they already are, like biometric recognition, such as fingerprints, retina scans, and voice patterns.

2FA authentication uses a combination of the above to provide security. 

Here is how this works, in the case of a website:

1. The website prompts the user to enter their login details. 
2. They enter their username and password – the knowledge factor. 
3. The website then prompts for the second step to complete the 2FA. 
4. They get a prompt to enter the 2FA code from their cell phone. 
5. They may get a prompt to scan their fingerprint, retina, etc. 
6. They provide the required factors, get verified, and access the website.

For example, 2FA looks like this at the airport:

• You present your passport at the airport counter for verification. 
• The airport official uses facial recognition software or does a retina scan. 
• The counter verifies you as the person travelling.

Once you decide to implement two-factor authentication in your application, these best practices will help you make the most of it.

• Enable 2FA for all users: Don’t provide 2FA for only a select group of users. Make it available for all users. 
• Disallow weak passwords: Set up a minimum password requirement. For example, a minimum of 8 characters, with a mixture of numbers, alphabets and special characters.
• Allow users to pick their authentication channel: Give your user the choice of more than two. For example, Google does this via text messages and an authentication app.
• Keep the format consistent: To make your use experience consistent, use similar 2FA code formatting. For example, avoid adding spaces in 2FA codes across all channels.

Next, we examine some common 2FA myths and whether they are real.

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What are the types of 2FA authentications?

Passwords or PINs, like we discussed earlier, can easily be guessed or stolen, especially if reused, weak or guessable. Some people use their birthdays, like 31 June 1993, which anyone can guess on the go. Some even use their first child’s name.

These factors make passwords or PINs the most vulnerable type of login access.

A scammer could easily trick you into tapping the forgot password button after following a pop-up and creating a new password, which is now visible to them due to the prompt you followed. That’s where a second factor comes into play.

There are about 10 different types of two-factor authentication you can add to support the password or PIN. We’ll skim through what they are, what they look like, and the user flow..

1. One-Time Password (OTP) via SMS or email (something you have)

What it is: The user enters his or her username or email, types the preset password or PIN (single-factor), and taps the “Log In” button. But before they’re granted access, they see a message on their screen that informs them that a code has been sent to their phone number, WhatsApp, or email, and that the code lasts for only a few minutes. That’s 2Factor authentication.

What it looks like: Receiving a 6-digit code like “229103” via SMS.

User flow:

• User logs in with their email/password
• Receives the OTP via email, WhatsApp, SMS, or in-app notification, then
• Enter it on the next screen, and they’re in.

Limitations:

• SMS can be intercepted or SIM-swapped
• Email accounts can be hacked
• Delays in delivery can frustrate users

Check out the best OTP SMS service providers.

3. Authenticator app (TOTP)

What it is: A time-based one-time password generated in an app like Google Authenticator or Microsoft Authenticator.

What it looks like: Opening the app and seeing a 6-digit code that refreshes every 30 seconds.

User flow:

• The user logs in with their email/password
• Opens the app to get the code, then 
• Enter the code on the login portal to complete the login process.

Limitations:

• If the phone is lost or reset without backup, access is lost
• Requires the user to install and set up the app

4. Biometrics (something you are)

What it is: Using physical characteristics like fingerprint, face, retina, or voice to verify identity.

What it looks like:

• Touching the fingerprint scanner on a device
• Scanning the face with the camera
• Saying a voice phrase

User flow:

• Attempt login
• Device prompts for a biometric scan
• Authenticates or denies access

Limitations:

• Not all devices support this
• Privacy concerns
• Not foolproof (face masks, wet fingers)

5. Hardware security keys (like YubiKey)

What it is: A small physical USB or NFC device that users must plug in or tap to verify login.

What it looks like: The user simply inserts the key into the USB port or taps it on the phone, and he has access.

User flow:

• Log in with a password
• Prompt appears
• Plug in or tap key
• Access granted

Limitations:

• Needs to be purchased
• Can be stolen
• Can be lost

6. Push notification approval (via authenticator app)

What it is: A user gets a notification on their trusted device (like a smartphone) asking them to simply tap “Approve” or “Deny” to confirm if they’re the same person trying to access the account at that time.

What it looks like: “Someone is trying to sign in. Was this you?”

User flow:

• Enter login details (username/email and password)
• Receive push notification asking to confirm “Yes, it’s me” or No, it’s not me”.
• The user taps “Yes, it’s me” and is granted access.

Limitations:

• Requires internet
• Risk of accidental approval or push fatigue

7. Security questions (something you know)

What it is: Pre-selected personal questions that only the user should know.

What it looks like: “What was the name of your first child?” Answer: “Daniel.”

User flow:

• User enters their password, then immediately
• They see the security/secret question they’d already set up while registering on the platform, with some input box to type their answer “Daniel”, as used in the example above. And they’re in.

Limitations:

• It’s easy to guess or find possible answers to that private question (they only need to spy on social media and look for posts you’ve made in the past about your first child, Daniel)
• It was more usable those years before Facebook became popular. The security standards in today’s world are different.

8. Email link verification (something you have)

What it is: Instead of entering a password, the user gets a login link sent to their email. Once they click on the link, they’re in.

What it looks like: “Click this link to log in to your account.”

User flow:

• The user enters their email address
• Opens their inbox, and
• Clicks the link. Voilà!

Limitations:

• If the email is compromised, the user is in big trouble
• Those links can expire
• The email could be duplicated by scammers monitoring your login and sent as a phishing email. Once you click on the link, they have full access. Only a few people in a setting can tell a fake email from the real one, so most will fall for this.

9. Behavioural biometrics (something you do)

What it is: this 2FA method is made possible with the improvements in artificial intelligence (AI), which notices how a user types, moves their mouse, or holds their phone while typing, then determines that this might not be the same person it’s used to.

What it looks like:

• Typing speed and rhythm
• Touch pressure
• Device tilt
• Device type

User flow: this analysis and the start of user behaviour happen silently in the background while the user is logging in or using the app.

Limitations:

• It needs AI/ML models
• This method is still emerging, and isn’t widely adopted yet as many people are still sceptical about AI and the limitations that should govern its use
• The data analysis and accuracy can be inconsistent, and can cause unnecessary tension for the user.

10. Location-based two-factor authentication (somewhere you are)

What it is: this method involves the AI feature of the platform analysing the consistency of the user’s location(s) and checking if the user is logging in from a usual location (city, IP address, or device).

What it looks like:

• Alert: “New login attempt from China. Is this you?”

User flow:

• User logs in from a known location = allowed
• According to users’ location changes per week, they’ve frequented certain limited locations in a particular province, area, state, or country.
• All of a sudden, there’s a login attempt from an unusual location. The system automatically blocks the unusual login and sends a message or email to the user’s phone or email address to confirm whether they’re the same person in that location or not.

Limitations:

• It may affect users who commute or travel often to different locations and who aren’t stuck with certain routes.
• VPNs can confuse the system about the real location of the user.

Why do you need two-factor authentication (2FA)?

Here is why:

• Humans (your users) have a bad recall, and many do not create strong passwords. A report on leaked passwords showed how hackers operate. They use ‘admin’ and ‘administrator’ to search for people’s passwords. 
• Your users have too many accounts, and remembering each password is impossible. This leads to password recycling. All it takes is to break one password, and they have access to other data.
• When data breaches occur, thousands of accounts get compromised. Hackers give away data on the dark web.
• Hackers find new and innovative ways to steal your users’ information. They can manipulate them into divulging information or use offline methods. They can guess their passwords and even use dictionaries to find their passwords.

So, to put it in one sentence, 2FA help you secure your application.

Now that we know why you need 2FA let’s explore how it works.

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So, which type of 2FA should you use?

For business owners like you who understand the implications that come with data breaches, I advise you to combine two or more of the strongest and most convenient factors.

• Password + Authenticator App
• Email Link + Fingerprint
• Password + Security Key

This way, even if one method is compromised, the attacker still can’t get in, as they’ll need the other methods to complete the login.

If you want to implement a secure and simple MFA system that uses OTPs sent over SMS or voice, check out SMSCountry’s SMS API. It’s a fast and dev-friendly solution that helps you send fast and secure one-time passwords (OTPs) to your users during sign-up, login, or transactions. 

What are the cons of two-factor authentication (2FA)?

Here are the drawbacks of using Two-Factor Authentication (2FA) for your mobile or web application:

• User inconvenience: It adds extra steps to the login process, which some users find annoying or time-consuming.
• Poor adoption rates: Many users avoid setting it up, especially if they don’t understand the importance of added security.
• Device dependency: Many 2FA methods require a secondary device (e.g., a phone or security key). Losing that device can lock users out.
• SMS vulnerabilities: Codes sent via SMS, although being the fastest and most affordable means for your organisation, can be intercepted through SIM swapping, phishing, or SS7 network flaws. This can only be solved when you use the most secure SMS service providers to send SMS to your users.
• App fatigue: Authenticator apps can be confusing to non-tech users, and managing multiple accounts can feel overwhelming.
• Limited offline access: Without an internet connection or mobile signal, receiving codes or push notifications might be impossible.
• Backup/recovery challenges: If users lose access to their second factor (e.g., phone reset), the recovery processes can be lengthy and frustrating.
• Compatibility issues: Some older applications or systems don’t support 2FA well, leading to integration problems.
• Security isn’t foolproof: While 2FA is stronger than SFA (passwords alone), sophisticated phishing attacks or malware can still bypass it.
• Operational overhead: IT teams may need to invest time in training, managing exceptions, and helping users recover locked accounts.

So, the question is…

Can 2FA be hacked?

The answer is, yes, Two-Factor Authentication (2FA) can be hacked.

While it adds a strong layer of protection beyond just a password, it’s not immune to attacks.

Here’s how hackers can bypass 2FA.

1. Phishing attacks in real time

Attackers can build fake login pages that look identical to real ones.

When a user enters their username, password, and even the 2FA code, the attacker captures everything and quickly uses those details to log into the actual site. This type of attack is often called real-time phishing or an adversary-in-the-middle (AiTM) attack.

2. SIM swapping

For 2FA systems that send codes via SMS, hackers can contact a mobile carrier, pretend to be the user, and convince the company to transfer the user’s phone number to a new SIM card. Once they gain control of the number, they start receiving the victim’s 2FA codes.

3. Malware and keyloggers

Malicious software installed on a user’s device can record everything they type, including passwords and 2FA codes.

Some advanced malware can even capture screen contents or extract data directly from authentication apps.

4. Man-in-the-browser attacks

These attacks involve malware that alters how the browser communicates with websites.

Even if the user successfully logs in with 2FA, the malware can silently perform unauthorised actions within that session.

5. Social engineering

Attackers can pretend to be a trusted party, such as a bank, tech support, or HR department, and persuade the user to share their 2FA code. 

These scams rely on creating a sense of urgency or fear to manipulate users.

6. Brute-force or replay attacks on weak systems

If the 2FA systems are poorly designed, they can cause unlimited logins or even the reuse of expired codes, which shouldn’t be. 

Attackers know this, that’s why they try to exploit these vulnerabilities by trying multiple code combinations or replaying previously used codes to see if the system doesn’t reject them.

But despite these vulnerabilities, 2FA remains more secure than one-factor authentication.

Now, let’s see how 2FA compares to MFA and passwordless authentication.

2FA vs MFA comparison

The table below summarises how 2FA stacks up against MFA.

Aspect	2FA (Two-Factor Authentication)	MFA (Multi-Factor Authentication)
How many factors?	Exactly 2	2 or more (no upper limit)
Security level	Stronger than a password, but fixed to two layers	Higher, can keep adding layers depending on risk
Flexibility	Rigid; always stops at two steps	Flexible; customisable per user, app, or risk level
Examples	Password + SMS codePIN + fingerprint	Password + fingerprint + smart cardFace ID + OTP + location
Common use cases	Basic apps, banking, and eCommerce	Corporate apps, admin dashboards, high-value transactions
User experience	Simpler, faster than MFA	May be slower or more complex, depending on setup

2FA vs passwordless authentication

Here’s how 2FA compares with Passwordless authentication.

Aspect	2FA (Two-Factor Authentication)	Passwordless Authentication
Use of passwords?	Yes, requires a password as one of the two factors	No; completely removes passwords
Login flow	Step 1: Enter passwordStep 2: Enter code from phone/email	Step 1: Tap fingerprint / click magic link / insert hardware key
Security level	Good, but still vulnerable to phishing, SIM swap, or reused passwords	Higher; less risk of phishing, keylogging, or credential leaks
User convenience	Moderate; extra step after password	High, fast, no need to remember anything
Tech requirements	Works on most platforms	May require newer devices or infrastructure (e.g., biometrics)
Examples	Gmail with password + OTPBank login with password + SMS code	Microsoft Hello, Apple Face ID, Magic login links, FIDO2 keys

Next, we examine some common 2FA myths and whether they are real.

3 myths of two-factor authentication 

Because implementing 2FA requires extra work. And because there’s ‘2’ written on it, you may have heard many assumptions about it.

Let’s look at three common ones.

Myth 1: 2FA requires two devices

It does not. One device is insufficient

This myth stems from the idea that 2FA becomes foolproof if done from two devices. For instance, entering your password via a laptop and using the phone to receive SMS. 

You don’t have to. 

You can do everything from one device.

Myth 2:  2FA diminishes the user experience

This idea stems from the perception that 2FA is a compliance rule and it doesn’t mitigate fraud risk. 

So you may be tempted to think two-factor authentication is an unnecessary step that makes it longer for users to access your application.

The truth is your users will love you more when they know you’re going the extra step to secure their privacy.

With the increase in cybercrimes, your users will appreciate anything that makes them feel safe using your platform.

Myth # 3 All 2FA authentication are the same and equal

They are not.

2FA technology has evolved since its first implementation. The earliest implementation relied on hardware tokens that people carried around. 

Since then, SMS authentication and phone calls have replaced hardware tokens. Also, some applications have tried using cryptographic information to authenticate their users.

And more.

Because you’re here, learn more about OTP.

So, you’ll agree with me that when you add two-factor authentication, your users feel safer. But if it’s slow or doesn’t even deliver at all? They’ll definitely drop off.

That’s why speed matters when you use 2FA in your application. And that’s where SMSCountry’s OTP SMS API comes in.

What is the SMSCountry OTP SMS API?

SMSCountry’s OTP SMS API lets you send one-time passwords to users in 5 seconds, anywhere in the world, with a deliverability rate of 99%. It’s secure, easy to integrate for developers, and built to scale with your business or organisation.

Want to see how we’d help you implement 2FA using our fast, secure and scalable API?
Schedule a demo, and our team will contact you ASAP. 

Frequently Asked Questions about 2FA

Does 2FA add a lot of security?

Two-factor authentication adds a layer of security. This makes it challenging for hackers to access online accounts and devices. Even if they get access to a password, they will need access to the 2FA authentication method to gain access.

Does 2FA have any limitations?

It is a reliable and effective system. Logging into a system is an extra step, adding time to the login process. It can be annoying for some users. It requires continuous maintenance and upkeep.

Is 2FA effective against phishing attacks?

2FA protects your account by providing you with two different forms of authentication. It helps protect your credentials. But if you decide to click on phishing links after verification, there is little 2FA can do for you. 

A better way to protect yourself from phishing is to educate yourself about it. Never give your information on unsecured sites, and change your passwords regularly. And don’t click on links out of curiosity.

Can hackers bypass 2FA?

Tech-savvy hackers will try and succeed in bypassing every security set-up in the world. So yes, it’s possible to bypass two-factor authentication also. They can do so by intercepting the communication as it happens. 
But all that said, it is safer to protect your account and enable 2FA than to leave your account unsecured. Unsecured accounts are easier to hack into as there is zero resistance.