What is CAPTCHA? It stands for Completely Automated Public Turing test to tell Computers and Humans Apart. It is a test that assists a computer in telling the difference between humans and machines, that has been trademarked by Carnegie Mellon University. With CAPTCHA a computer can detect whether a machine or a person completed a test, and discard any computer answers.



It works on the assumption that humans can read distorted machines but machines usually cannot do so. You can know more about CAPTCHA and smart CAPTCHA at http://www.protectwebform.com/ and http://www.protectwebform.com/smartcaptcha.

Most website owners find CAPTCHA very useful. Such tests help to prevent programs known as bots. Bots are programs that pretend to be humans and abuse the services of the internet. Bots try to sell or make you sign up for thousands of free mail services. The bots spam your inbox daily. They intrude into common chat rooms to accumulate 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.

CAPTCHAS and CAPTCHA plug-ins (http://www.protectwebform.com/plugin_wordpress) intend to prevent these bots from creating havoc. The CAPTCHA programs need the user to recognise and then key in a string of distorted letters and numbers in a box. The string will appear as a distorted image over a ?noisy? background. CAPTCHAs are used by various large and small sites. You will find them in mail services, banking sites, blogs, chat rooms and similar places.

Spammers send unsolicited messages in bulk to you inbox. These messages are not desirable at all. The most common kind of spam is email spam. However there can be other spam too in the form of usenet newsgroup spam, log spam, search engine spam, instamessaging spam and similar others.

Advertisers resort to spamming as spamming does not incur any kind of operating costs other than the cost of managing the list of individuals that are targeted to receive the mails. Also you cannot hold the sender accountable for the mass mailers they send. Since there is no entry barriers, spamming has become really ubiquitous. This is the reason why all your inbox is so inundated with mass mailers whenever you access them.

Usenet spam is a message that can be sent to twenty or more Usenet newsgroups. This kind of spam is usually targeted to those people who visit and read the newsgroups but do not post anything or give any kind of address. This kind of spam inundates the newsgroups with unnecessary advertisement and posts. It also challenges the owner's ability to accept and manage the topics on the system.

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.