CAPTCHA or the Completely Automated Public Turing test to tell Computers and Humans Apart is widely advertised but one wonders if it is really useful or not. But, before we discuss its practical utility, let us see what CAPTCHA is all about. It is a test, which helps the computer to distinguish between machines and human beings. It creates and grades tests that automatically accept all humans and reject all machines.

It gives you a test to decipher distorted numbers and letters, which are pretty easy for a person to do, but cannot be figured out by a machine. For further details about CAPTCHA and smart CAPTCHA go to and

CAPTCHAs are really useful. They help preventing programs known as bots. Bots are programs that pretend to be humans and abuse the services of the internet. Bots usually have the intention to sell or make you sign up for thousands of free mail services. The bots spam your inbox daily. They penetrate common chat rooms with the intention of accumulating personal information and publishing links to various sites for promotional benefits.

The bots create worms that can cause immense harm to your machine. They crack your passwords, assault privacy and use your personal information for commercial use without your permission.

CAPTCHA is a sure shot way of preventing these bots from creating havoc. The CAPTCHA asks the user to recognize the distorted image of letters and numbers usually with a string over a ‘noisy’ background. While it is easy for a human to decipher it, the machine usually cannot. And, that is how CAPTCHA distinguishes between a human user and a computer. Various large and small sites find CAPTCHA quite useful. No wonder, you see them in mail services, banking sites, blogs, chat rooms and similar places.

Spammers send unsolicited, undesirable and unwarranted messages in bulk to your inbox. Besides that, there can be other spam too in the form of usenet newsgroup spam, log spam, search engine spam and the like.

Some advertisers think spam is a good way to go to get their message out to the masses. It doesn’t really cost them anything other than finding lists of e-mail addresses to send to, so they send mass amounts of mailings, and there is nothing you can do about to stop it, because laws do not allow holding a sender responsible for the number of mailings they send on the internet.

On newsgroups, the spam is Usenet Spam. You may have seen this when you log into a newsgroup you enjoy. You may be trying to read a topic but see that is has been inundated with post after post of some sort of advertisement that doesn’t belong there. That’s Usenet spam.

Another kind of spam, which is a little more expensive, is the instant message spam. In this case, advertisers have paid a little more to get a hold of a list of instant messaging ID’s and then sent messages directly to those people.

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About the Article Author

Oleg is an expert on CAPTCHA design and development. Click to find out more about his new CAPTCHA Plugin technology.

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