Telegram Bot Captcha protection

What is Captcha?

A CAPTCHA test is used to identify whether an internet user is a human or a bot. CAPTCHA is a short form for “Completely Automated Public Turing Test to Distinguish Robots from People.” On the Internet, CAPTCHA and reCAPTCHA tests are frequently encountered. Such tests are supposed to ensure that content is accessed by humans, not robots, as bots usually can’t resolve captcha.

You can usually see the captchas on the internet when you try to log in to a website. It could be a simple test asking you to solve math problems, or more complex to mark the pictures showing specific objects or use the slider to place one thing within another. The test itself is usually written in JavaScript to make it more difficult for automated bots to solve it as support for JavaScript is a rather advanced topic, eliminating most of the not-professional bot farms trying to guess your password or register thousands of accounts.

Captcha and Telegram users

There are thousands of shady businesses offering hundreds of thousands of fake and spam Telegram accounts in their portfolio. These accounts are used to send spam messages to Telegram users, and usually, everything starts with the accounts joining the group. There are few spam bot code repositories available publicly, so we’ve looked at them and analysed how they work. We learned during the process that the developers who created those accounts were not only not too skilled but had done it in the laziest way possible.

Check our “How to stop bots on telegram” page for more information.

Telegram Bot Captcha and our approach

We know that our bots operate in thousands of groups, with dozens of different languages used. Some users may have a different language keyboard installed on their phone, and presenting them, for example, with a captcha in English can be problematic if their phone language is set to Arabic or Russian. We also know and understand that new users of your group could be potentially deterred by the advanced challenges - for example, mathematical or even finding appropriate words to resolve the captcha.

We made things as easy to use and understand as possible ( if your user is not a bot, of course! )

As you can see the user is presented with a simple button in the language, you’ve set for your group. Everyone can press the button, but only the user to who this button was dedicated can trigger the action.

Captcha function setup

• You can enable captcha mode for your telegram bot in the “Group Settings / Bot” section of your bot panel.
• We strongly advise you to set the function kick user if captcha is not solved to enabled. This will allow the bot to automatically eliminate users who don’t solve the captcha.
• Set the timer to your liking. We recommend setting it to at least five minutes to give users enough time to check your group messages and figure out if they want to stay.

How does it work

This is step by step of Captcha Mode for your group.

• User joins the group either by invitation link or being added by another user.
• Our bots detect the new user and set up long-lasting restrictions for him, preventing the user from sending anything into the group.
• Bot then sends a message to the group asking the user to press the button to confirm they’re a human.
• Timer in the background starts, so the user ( in our example ) has 5 minutes to press the button.
• If they’re successful
  • Bot removes all the restrictions for the user.
  • If you have a greeting set up for your group, the bot displays the greeting to the user.
  • They can participate in discussions in your group
• If they’ve ignored the captcha ( or can’t click it because they’re a bot ) after 5 minutes timer expires - they’re kicked out from the group.

Is it effective in fighting spam?

We have observed, on average 95% reduction of the spam in groups where captcha mode is enabled.
The remaining 5% are either actual spammers with live accounts or accounts which joined before the captcha mode was enabled and were activated by their owners.