Engineering
5 Common TOTP Mistakes Developers Make (and How to Fix them)
Fung
August 28, 2025
Two-factor authentication (2FA) with one-time passwords (OTPs) is supposed to keep accounts secure. But in recent years, attackers have started using OTP bots—automated fraud tools that trick users into giving up their codes and abuse SMS systems at scale. For developers, these bots create not only a security risk but also a financial risk, as shown by Twitter’s $60 million/year loss from SMS fraud.
This article explains what OTP bots are, how they operate, and how developers can defend against them with better architecture and modern security tools.
What Is an OTP Bot?
An OTP bot is malicious software or a service that automates the theft or abuse of one-time passwords. Unlike simple brute-force bots, OTP bots are designed to phish OTP codes in real time and relay them to attackers, allowing them to bypass multi-factor authentication.
In other words, the otp bot meaning is simple: it’s a bot that targets the very security layer (OTP) that was meant to stop intrusions.
How OTP Bots Work
Most OTP bot attacks follow a similar flow:
- Attacker has stolen user credentials (username/password).
- OTP bot initiates contact with the victim, usually via automated phone call or SMS.
- The bot impersonates a trusted service (“This is your bank’s fraud department, please verify your code”).
- The victim receives a real OTP and unknowingly gives it to the bot.
- The bot relays the OTP to the attacker in real time.
Modern otp bot apps are available for rent on Telegram or underground forums. They advertise features like:
- Caller ID spoofing to appear legitimate
- Multi-language support
- Real-time OTP relay
- Bulk attack automation
For developers, the danger is that these “apps” scale attacks effortlessly. One attacker can run hundreds of simultaneous OTP phishing calls without lifting a finger.
Why OTP Bots Are a Threat to Developers
- Security Risk: OTP bots undermine the trust users place in 2FA. Account takeover becomes trivial once the OTP is stolen.
- Financial Risk: Bots trigger fraudulent SMS requests, leading to SMS pumping fraud—where attackers abuse your OTP system to rack up telecom charges.
- Operational Risk: Bots flood authentication endpoints with fake OTP requests, draining resources and overwhelming your infrastructure.
Common Myths About OTP Bots
- Myth 1: “OTP software is secure if it uses SMS.”
- Reality: SMS is the weakest link. OTP bots exploit it with ease.
- Myth 2: “Only banks are targeted.”
- Reality: Any app with OTP-based 2FA is a target—e-commerce, SaaS, fintech, even gaming platforms.
How to Stop OTP Bots
Developers can harden OTP flows with layered defenses:
- Rate limiting & monitoring → Detect abnormal OTP request spikes.
- CAPTCHAs → Force human verification before OTP requests.
- Fraud detection → Use machine learning to detect patterns of OTP abuse.
- Alternative MFA methods → WebAuthn, passkeys, and push-based MFA are resistant to phishing.
These are all supported by Authgear out of the box.
Should Developers Worry About Free OTP Bots?
Yes. Many otp bot free services circulate on Telegram and Discord. They claim to offer “free trials” of OTP phishing bots, lowering the barrier for rookie attackers.
For developers, the takeaway is clear: if attackers can get free bots, your app could be attacked at zero cost to them. Meanwhile, you bear the infrastructure and fraud bill.
Building Bot-Resistant OTP Systems with Authgear
Instead of building anti-bot defenses in-house, Authgear provides developer-friendly tools that secure OTP flows:
- CAPTCHA support: Stops automated OTP requests before they start
- Fraud detection: ML-powered detection to block suspicious OTP traffic, e.g. impossible-travel, known high-risk fingerprint.
- Rate limiting & device intelligence: Catch bots before they drain your system
Conclusion
OTP bots are a growing threat to developers building authentication systems. They’re cheap, scalable, and effective at bypassing SMS OTP security. Left unchecked, they can drain both your users’ trust and your company’s finances.
The solution is proactive defense: rate limiting, CAPTCHAs, fraud detection, and moving beyond SMS OTP where possible. With Authgear’s built-in protections, developers can secure OTP workflows without reinventing the wheel.
Start protecting your app today with Authgear.
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FAQ
What is an OTP bot?
An OTP bot is malicious software that automates the theft of one-time passwords. Instead of brute-forcing codes, it tricks users into revealing them (often via fake calls or SMS) and relays them to attackers in real time.
How do OTP bots bypass two-factor authentication (2FA)?
OTP bots exploit the weakest part of 2FA: the human user. When a victim receives a real OTP code, the bot—posing as a trusted service—asks them to share it. The bot then instantly forwards the code to the attacker, bypassing SMS-based 2FA.
Why are OTP bots dangerous for developers?
OTP bots create both security risks (account takeovers, data theft) and financial risks (SMS pumping fraud where attackers trigger costly OTP requests). They also stress infrastructure with fake traffic, making authentication unreliable.
How can developers stop OTP bots?
To block OTP bots, developers should:
- Add CAPTCHAs or proof-of-work challenges before sending OTPs
- Rate-limit and monitor OTP requests
- Detect anomalies with fraud detection (e.g., Authgear SMS pumping protection)
- Consider stronger MFA like WebAuthn or passkeys
Are free OTP bots a real threat?
Yes. Free OTP bot tools circulate on Telegram and underground forums. Even rookie attackers can use them to bypass 2FA at zero cost. Developers should assume these bots exist and harden their OTP workflows accordingly.
