Nowadays, a simple checkbox to confirm that you are not a robot can become a digital trap. Although CAPTCHA Although they emerged as a legitimate measure of protection against bots and automated access, cybercriminals have learned to forge them with dangerous skill. Fake CAPTCHAs are a gateway for malware.
We are facing a sophisticated deception technique that has already affected thousands of people. Using pages designed to appear legitimate, attackers convince users to execute commands, install software, or click malicious links. All this occurs under the guise of a simple security check.
What is a CAPTCHA and how is it supposed to work?
A CAPTCHA (acronym for Completely Automated Public Turing test to tell Computers and Humans Apart) It is a system that allows distinguish between real people and bots. It manifests as visual or logical tests that a human can easily solve, but are complex for an algorithm, such as selecting images with traffic lights or writing distorted letters.
Its traditional function is protect digital platforms from automated access, mass attacks or spam. Google, for example, uses reCAPTCHA on millions of websites to block automated attacks and ensure service integrity.
How do hackers use fake CAPTCHAs?
Cybercriminals have noticed that this tool has become so common that users don't even question its authenticity. This has opened up a dangerous avenue: mimic legitimate CAPTCHAs to install malware on unsuspecting devices.
The process usually begins when the Internet user visits a suspicious website or clicks on a malicious link. A seemingly normal CAPTCHA appears, but it's actually fake. When the user interacts with it, whether by checking a box, copying a code, or following instructions, a malicious download is activated in the background. This is one of the reasons why it's important to have an updated antivirus that can detect and prevent these threats.
The phenomenon is not theoretical. Authorities such as the National Police and cybersecurity companies such as Kaspersky or CSIRT-CV have already issued official alerts. on the consequences of these attacks.
According to Kaspersky, from September to October 2024, more than 140.000 interactions with malicious ads redirecting to fake CAPTCHAs were detected, while nearly 20.000 users were redirected to fraudulent pages after clicking on these ads. Spain is among the most affected countries, along with Brazil, Italy, and Russia.
Types of associated malware
Fake CAPTCHAs not only deceive, but also act as vectors for highly sophisticated malware. Among the most frequently detected are:
- Lumma Stealer: A malware type stealer aimed at stealing data stored in the browser, including passwords, sensitive files, and banking data.
- SecTopRAT: A remote access Trojan (Remote Access Trojan) that allows attackers control the user's system remotely and extract data without the victim noticing.
Where do these fake CAPTCHAs usually appear?
These attacks are not limited to dark or dubious websites. While many appear on Untrustworthy portals, download sites, gambling sites, or adult content, have also been found on seemingly legitimate sites that were previously compromised.
In addition, hackers have perfected their interfaces. until these are almost identical to real CAPTCHAs, even imitating the typical error messages of the Chrome browser or the Windows operating system.
How do these fake CAPTCHAs trick us? These are the steps involved:
- Malvertising: The user clicks on an ad that doesn't seem suspicious.
- Deceptive redirection: That click takes you to a fraudulent website that displays a fake CAPTCHA.
- Dangerous instruction: The site asks you to copy and execute a command in the terminal, PowerShell, or browser.
- Infection: Malware is downloaded and executed, stealing information or allowing remote access.
Why does this scam work?
The key to the success of these attacks is the automatic trust that users have in CAPTCHA systems. Furthermore, this type of interaction (checking "I'm not a robot") has become so routine that many people ignore the context. This lack of attention is what cybercriminals exploit.
Even fake CAPTCHAs have been detected that do not require suspicious clicks or visible downloads.. Simply follow a textual instruction for the malware to activate.
How to detect a fraudulent CAPTCHA
There are some signs that a CAPTCHA could be fake:
- Presence in unusual places: If it appears on a page that shouldn't need it, be suspicious.
- Strange instructions: A legitimate CAPTCHA will never ask you to copy and paste commands into your computer.
- Automatic redirects: If you are redirected to another website after interacting with the CAPTCHA, close the tab immediately.
- Too rudimentary or too polished aesthetics: An unusually well-crafted or misspelled CAPTCHA can be a red flag.
What to do if you've fallen for the scam
If you suspect that you may have interacted with a fake CAPTCHA, you should act immediatelyChange your passwords, disconnect your device from the internet, scan your computer with an antivirus, and, if necessary, contact your bank or cryptocurrency provider.
Fake CAPTCHAs are not just a new trend in digital crime, but a real threat that is growing and evolving rapidly. What seems like a simple check can be the prelude to an attack on your privacy, finances, and online security. Therefore, paying attention to details, staying up-to-date, and protecting your devices with the right tools can make the difference between browsing safely or falling into a trap.