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 http://www.protectwebform.com/ and http://www.protectwebform.com/smartcaptcha.

Having a CAPTCHA installed can protect against bots, which are programs that can repeatedly spam inboxes, try to post and retrieve personal information in chatrooms, and also try to get e-mail addresses and other information to use for promotions to sell services or items, or sign you up for numerous free mail services.

In addition these bots can put a worm on your system, getting your passwords, and other personal information and taking it back to the Internet for others to use commercially without you even knowing how they got it.

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.

There is another kind of email spam that targets individuals with direct messages. It scans postings from Usenet or pilfers from the Internet mailing list. This kind of spamming involves some expenditure.
About the Author

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