If you run a blog, forum, or any type of website that solicits user comments, you run into spammers. In my case, most spammers do not seek to post on the forum, however they just want to register their account and update their profile with a website. The reason being is, more incoming links to their website results in a higher ranking in search engines. Most of the time, they individuals are not promoting their website, they are hired by someone to get them x amount of incoming links.
I have been running visual verification (captcha image), since the beginning of the forum. Last year I added a couple logic questions and while I have greatly trimmed the spam, I still get a few registrations. I decided to take it a step further and use Google’s recaptcha tool. Essentially it uses a more sophisticated image that prevents it from being read correctly by computers. It is not fool proof, spammers can also use human power to decipher the correct letters, however this greatly slows down the process for them.