CAPTCHA: Stands for Completely Automated Public Turning Test to Tell Computers and Human Apart. It is used to ensure that the form is filled by Human Being.Its actually a form of protection from computers(bots) filling out forms.
There are many different kinds of "captcha's" some are Image recognition type, another type is like "result of sum of two numbers or any operation" eg:-"2+5-5".
You may be thinking, Why any computer will fill the form? and anyway why we need the need to worry for that?
Protecting from multiple registration:-
Using such Bots one can sign up 1000 of accounts in a minute. Which makes server busy(DoS attack i.e indefinite request to server which leads to Denial of Service by the sever) and unnecessary loss of storage area.
Preventing Comment Spam in Blogs:-
Sometimes to increase the search engine rank programmer use bogus comment generator(a kind of bots), which is akind of comment spam. But by using CAPTCH only Human can enter the comment.
Preventing Dictionary Attacks:-
A program can iterate through entire range of combination till password match is found, but many websites today includes CAPTCHA after some unsuccessful login attempt. The idea behind this is computer does'nt understand "captcha"and therefore iterate further.
Is it secure?
Decoding images of distorted text, for instance, is well beyond the capabilities of modern computer. To deface this one must work on advanced field of Artificial Intelligence.
There are many different kinds of "captcha's" some are Image recognition type, another type is like "result of sum of two numbers or any operation" eg:-"2+5-5".
You may be thinking, Why any computer will fill the form? and anyway why we need the need to worry for that?
Protecting from multiple registration:-
Using such Bots one can sign up 1000 of accounts in a minute. Which makes server busy(DoS attack i.e indefinite request to server which leads to Denial of Service by the sever) and unnecessary loss of storage area.
Preventing Comment Spam in Blogs:-
Sometimes to increase the search engine rank programmer use bogus comment generator(a kind of bots), which is akind of comment spam. But by using CAPTCH only Human can enter the comment.
Preventing Dictionary Attacks:-
A program can iterate through entire range of combination till password match is found, but many websites today includes CAPTCHA after some unsuccessful login attempt. The idea behind this is computer does'nt understand "captcha"and therefore iterate further.
Is it secure?
Decoding images of distorted text, for instance, is well beyond the capabilities of modern computer. To deface this one must work on advanced field of Artificial Intelligence.
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