While reports that online porn sites offering free access when the visitors enter the right response to a Captcha secured entry field have been around for a while (see for example BoingBoing 2004 ) with recent rises in spam originating from Google, Yahoo or Hotmail accounts the discussion on that topic is on again.
Captchas or “Completely Automated Public Turing test to tell Computers and Humans Apart” that are within these relay attacks defeated by visitors to the intermediate (porn) site are seemingly often used to create free users accounts with online mail services in the background. And these newly created account are later the source for sending out spam that in many cases can not easily filtered out (which admin would blacklist the Google-Mail-Server).
We have recently seen that a similar approach is also used to create user accounts on software development sites like sourceforge etc.
Click on the image below for the link (blog post)
Thorsten Holz has put a short video on his blog to demonstrate the technique. He also warns users not to go to the original (porn) site as the HTML contains a malicious iframe.
More information:
Thorsten Holz’s Honeyblog
Roaring Penguin on captcha cracking
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