The problem with SMS OTPs: Why this 2FA method isn’t as secure as you think

Every day, millions rely on SMS one-time passwords (OTPs) for logging into services, verifying identities, or authorizing transactions. While SMS OTPs have become the most popular two-factor authentication (2FA) method due to their convenience, they are far from secure. Cybercriminals exploit their vulnerabilities through phishing, social engineering, and other fraud techniques, putting users at risk of identity theft and financial loss.

The security flaws in SMS OTPs

SMS OTPs are widely used because nearly everyone has a mobile phone, making it a straightforward way to add a second authentication factor. However, SMS was never designed with security in mind. Messages can be intercepted, spoofed, or manipulated, enabling hackers to perform account takeovers (ATOs).

Common attacks on SMS OTPs

Smishing (SMS Phishing)

Smishing is a phishing attack via text messages. Fraudsters send fake messages pretending to be from banks, retailers, or service providers, urging recipients to enter their login details or OTPs on a malicious website. Once submitted, attackers gain full access to victims’ accounts. Smishing has been behind several high-profile security leaks, including the 2022 Activision data breach.

Man-in-the-middle (MITM) attacks

Since SMS lacks encryption, cybercriminals can intercept messages using malware or rogue networks. Hackers have developed botnets that infiltrate telecom systems, allowing them to read messages, track locations, and steal authentication codes without users’ knowledge. 

Automated bots and phishing kits

Researchers from Stony Brook University found over 1,200 phishing kits designed to steal 2FA codes in active use. Attackers use automated bots to trick users into providing their OTPs, enabling fraudulent transactions and unauthorized access. Vice’s Motherboard spoke to a seller who boasted that these bots can be used by anyone – even if they don’t have social engineering skills.

SIM swap fraud

One of the most dangerous threats is SIM swap fraud. Attackers trick mobile carriers into transferring a victim’s number to a new SIM card under their control. This allows them to receive all OTPs sent to that number, bypassing 2FA entirely. SIM swap fraud has led to major breaches and financial losses worldwide.

SMS spoofing

Hackers manipulate sender information to make messages appear as though they are from a trusted source. This technique is commonly used in banking scams, where victims unknowingly enter their credentials on fraudulent sites, allowing attackers to access their accounts.

SMS pump fraud: the $6.7 billion scam

SMS pump fraud, also known as artificially inflated traffic (AIT), is a scheme where fraudsters work with insiders at telecom providers to generate massive amounts of SMS traffic to premium-rate numbers. Businesses footing the bill for these fraudulent messages lose billions annually.

In January 2023, Elon Musk claimed Twitter lost $60m to SMS pump fraud. In 2024 it was reported that as many as 35 billion fraudulent messages were sent by bad actors across 2023, costing businesses $1.16 billion.

Why SMS OTPs are no longer effective

Beyond security risks, SMS OTPs create friction in the user experience. They require extra steps, leading to delays and frustration, which can cause users to abandon transactions. Additionally, since OTPs can be copied, forwarded, and phished, they fail to provide strong security

The future of authentication: Silent Network Authentication

A better alternative is Silent Network Authentication (SNA), which leverages the cryptographic security of SIM cards and mobile networks for secure, seamless authentication. Unlike OTPs, this method is resistant to phishing, MITM attacks, and SIM swap fraud.

How it works

SNA uses a secure, encrypted connection between a mobile device and the network operator to verify the user’s identity. This eliminates the need for OTPs while ensuring that only the legitimate user can access their account.

Key benefits of Silent Network Authentication

• Secure & resistant to fraud: Unlike SMS OTPs, SNA cannot be phished, intercepted, or spoofed.
  
• Seamless & frictionless: Users authenticate automatically without manually entering codes, improving the customer experience.
• Universal & scalable: Works with all mobile networks and devices, requiring no special apps or hardware.
• Eliminates SMS Pump Fraud: Since authentication doesn’t rely on SMS, businesses avoid unnecessary costs from fraudulent traffic.

A smarter, safer future

The limitations of SMS OTPs make them an outdated solution for authentication. Silent Network Authentication offers a more secure and user-friendly alternative, leveraging the built-in security of mobile networks. It’s already in use and available for businesses looking to enhance security while simplifying the login experience.

To learn more about how Silent Network Authentication from IDlayr can protect your business, contact us today.