CAPTCHA Code: what it is and how it works

Table of contents

• What is a CAPTCHA code? 
• How a CAPTCHA test works?
• The benefits of using CAPTCHA
• The limitations of CAPTCHA: accessibility, security, and risks
• Evolution of CAPTCHA 

In this article, we will explore what a CAPTCHA code is, how it works, and what its advantages and limitations are. We will analyze its role in cybersecurity, why it is used, the associated risks, and the new developments in its evolution. 

What is a CAPTCHA code? 

The term CAPTCHA is an acronym for “Completely Automated Public Turing test to tell Computers and Humans Apart.” It refers to a system designed to distinguish human users from automated bots.

It was introduced in the early 2000s by a team of researchers at Carnegie Mellon University, led by Luis von Ahn, to combat the abuse of online services. 

The logic behind CAPTCHA is inspired by the Turing Test, created by mathematician Alan Turing to determine whether a machine could replicate human intelligence. Similarly, a CAPTCHA test challenges users to recognize distorted text, images, or other tasks that are difficult for bots but easy for people. 

How a CAPTCHA test works? 

CAPTCHA codes have become a cornerstone of cybersecurity due to their ability to protect online platforms from various types of automated attacks. Let’s take a closer look at the main benefits they offer. 

Protection against automated bots 

One of the most evident advantages is their ability to block bots—automated software programs that attempt to interact with websites as if they were real users. Bots can: 

• Register fake accounts on social media platforms or e-commerce websites;

• Send massive amounts of spam through contact forms or blog comments;

• Collect sensitive data or perform scraping attacks on content published by a search engine.

By using CAPTCHA, websites can filter out these harmful activities, allowing only human users to access services. 

Prevention of DDoS attacks 

DDoS (Distributed Denial of Service) attacks are among the biggest threats to websites. They involve overloading a server with automated requests, making it unusable for legitimate visitors.

By implementing CAPTCHA tests, websites can limit the number of automated requests from bots, protecting their infrastructure. 

Example
Many platforms trigger a CAPTCHA when they detect an unusually high level of activity from a specific IP address to determine whether the user is human. 

Reduction of online fraud 

Another major benefit of CAPTCHA codes is their ability to prevent fraudulent activities, such as: 

• Automated registrations to exploit promotions or discount coupons;

• Large-scale login attempts using “credential stuffing” techniques, where bots try different username and password combinations;

• Unauthorized access to restricted resources, such as paid content or event tickets. 

By implementing CAPTCHA, platforms can ensure that only human users gain access to these services, reducing financial losses caused by fraud. 

Improvement of website traffic quality 

CAPTCHA help improve the overall quality of website traffic by eliminating non-authentic interactions. This is especially useful for businesses and platforms that rely on metrics like user engagement and content interactions. 

Example
On a blog, it prevents bots from filling the comments section with spam, improving the user experience. Or on e-commerce sites that reduces fake requests that could skew sales analysis. 

Protecting a website’s reputation 

A website that suffers from bot attacks or spam can lose user trust. By implementing CAPTCHA, businesses can significantly reduce the risk of abuse and enhance the perception of their platform as secure and reliable.

This is crucial for industries handling sensitive data, such as online banking or digital healthcare services. 

Effectiveness for multilingual and international websites 

CAPTCHA are highly versatile and can be implemented in any language and customized to suit specific contexts. In developed markets, where online services are widespread,CAPTCHA serve as a crucial security measure.

However, they can also be effective in emerging regions, as long as they remain accessible to local users. 

Customization and continuous updates 

New CAPTCHA technologies, such as image-based CAPTCHA and invisible CAPTCHA, offer a better user experience while reducing effort.  For example: 

• Invisible CAPTCHA analyze user behavior (such as mouse movements or typing speed) to determine if they are human, eliminating the need for explicit actions;

• Image-based CAPTCHA are more interactive and engaging than traditional distorted text challenges. 

The benefits of using CAPTCHA

The adoption of CAPTCHA codes provides numerous cyber security advantages: 

• Bot protection
  Prevents automated registrations and logins, reducing spam and fraudulent activities. 

• Defense against DDoS attacks
  Limits excessive use of resources by bot networks. 

• Verification of human users
  Reduces the risk of fake accounts on social media, forums, and online services. 

• Search engine aecurity
  CAPTCHA help prevent bots from unauthorized indexing of website content. 

A well-known example is image-based CAPTCHA, such as selecting traffic lights in a grid—a challenge that remains effective against sophisticated bots. 

The limitations of CAPTCHA: accessibility, security, and risks 

Despite their usefulness, CAPTCHA codes have several limitations: 

• Accessibility issues
  Users with visual or cognitive disabilities may struggle to complete the test. 

• Challenges in emerging markets
  In countries with lower digital literacy, captchas can be an obstacle for users. 

• Potential for circumvention
  Advanced AI technologies enable bots to bypass some types of CAPTCHA. 

• False positives
  Even human users can fail the test due to reading errors or distractions. 

A particularly dangerous trend involves fake CAPTCHA scams, as seen in recent cyberattacks in Italy. These attacks trick users into completing seemingly legitimate tests, only to install malware like Lumma, which is designed to steal sensitive data. 

Evolution of CAPTCHA 

The future of CAPTCHA focuses on more sophisticated and user-friendly solutions.

Example
The invisible CAPTCHA , which analyzes user behavior on a webpage to determine whether they are human—without requiring them to complete a visible test. 

Additionally, image-based CAPTCHA continue to evolve to counter the advancements in AI-driven bots. However, the challenge is to balance security with ease of use to ensure a positive experience for human users. 

Questions and answers

1. What is a CAPTCHA code? 
   It is a system that distinguishes human users from automated bots using a test. 
2. What is its purpose? 
   It protects online platforms from abuse, spam, and cyberattacks. 
3. How does it work? 
   It requires users to complete challenges, such as recognizing images or entering distorted text. 
4. Why are CAPTCHA important for security? 
   They prevent bots from accessing online services, safeguarding data and resources. 
5. What are the limitations of CAPTCHA? 
   Accessibility issues for users with disabilities and vulnerability to advanced bots. 
6. What is a fake CAPTCHA? 
   It is a cyberattack that uses fake tests to spread malware or steal data. 
7. Who invented the CAPTCHA? 
   It was developed by a research team at Carnegie Mellon University led by Luis von Ahn. 
8. How do captchas protect search engines? 
   They prevent bots from indexing content or misusing search engine services. 
9. What is an invisible CAPTCHA? 
   It is a version that analyzes user behavior to verify humanity without a visible test. 
10. What risks are associated with fake CAPTCHA? 
    They can install malware or steal personal data by tricking users with fraudulent tests.