What is a CAPTCHA?


Why do I get those pictures of wavy blurry distorted text that I have to type into a box before I can log in to a web site?


Most web sites that offer a service, such as email, banking, social networks etc, require you to log in before you can use that service. The login process is generally: enter a username and password and then click a button. Easy right? So easy in fact that you could write software to do it for you. Go to a web site, enter a username and password, click a button. Simple.

The problem is that the people that found automating the login process useful were not the kind of users most sites wanted frequenting their sites. For example, a spammer might use such a program to automatically log in to a webmail web site and send thousands of emails before logging out and moving on to the next scripted login on another webmail web site. Or maybe someone offering a data presentation service may use automated logins to log in to other web sites, access useful data to use on their own site and then log out without contributing anything to that site. And all in a few seconds and without the need for a real person to do anything.

To combat this sort of automated activity security gurus started coming up with ways to check that it is a person, a human being, that is logging in and not an automated program. One of the most popular solutions was to show the person logging in a picture of some blurry text that they should be able to read, but an automated program should not. This was known as a CAPTCHA.

So that's why we are seeing these wavy words when we try to log in to our favourite sites. We are being tested to see if we are a human and not a computer program.

Last word

So next time you come across one of these CAPTCHAs you will know that this web site wants to restrict access to people only and not automated logins.

CAPTCHA stands for: Completely Automated Public Turing test to tell Computers and Humans Apart.

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Article date: 22nd February 2011

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