If you have spent much time on the web, you have probably encountered a captcha ("Completely Automated Public Turing test to tell Computers and Humans Apart"). These are those boxes of barely readable letters in strange colors and contortions that you are asked to type in to prove that you aren't an automated computer script angling for another hotmail account.
Well, the spammers who try and crack these so they can try and sell you a cheap rolex have found a great incentive. Free porn:
The ingenious crack is to offer a free porn site which requires that you key in the solution to a captcha -- which has been inlined from Yahoo or Hotmail -- before you can gain access. Free porn sites attract lots of users around the clock, and the spammers were able to generate captcha solutions fast enough to create as many throw-away email accounts as they wanted.
You can read more here.