A lot of unwanted mails you get as spams, previously it was only due to the mailto: format and occured mostly when you have put your mail id directly on the webpage. To avoid flooding of queries by sudden automatic filings and un-solicited subscription requests are the examples of bots/programs using your sites forms.
Now the solution for Webmasters ?
The Answer is CAPTCHA.
What is CAPTCHA ?
A "CAPTCHA" stands for "Completely Automated Public Turing test to tell Computers and Humans Apart", trademarked by Carnegie Mellon University, and is a free service. Mellon University Members Luis von Ahn, Manuel Blum, Nicholas J. Hopper along with John Langford of IBM are credited for coining the term CAPTCHA in 2000.
How CAPTCHA work?
The differentiation method between humans and computers (basically programs) is based on the visual and understandable logic. What you will see is a distorted image containing a twisted or random word-characters which are very hard for programs to distinguish. This stops them to move ahead as words don't match in guessing!!So far CAPTCHA has posed a big problem for spammers and a boon to genuine websites.
CAPTCHA For Puzzle Websites?
Created by Vohn Ahm and Blum in 2000 for yahoo, the puzzles website CAPTCHA has come a long way from simple distortion, to adding angled lines, to double puzzling, to bilingual to plain weird.
Use of CAPTCHA and Search Engine Optimization?
Search bots can't read forms, so no program including "Googlebot" can travel beyond your forms. The pages beyond the forms will not be indexed in search engines due to restricted access. Considering the benefits of no-spamming , a CAPTCHA all the way is a good way to use.
Resources:
- The Image Image Verification tutorial shows how to write your own Captcha implementation using PHP.
- Lanap BotDetect is a commercial solution for ASP and ASP.Net
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