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Spammers Tempt Surfers to Help Solve Captchas

Call it an online game of strip poker, only spammers are the ones walking away with all the winnings.

The latest innovation in malicious software takes the form of shapely "Melissa," an alluring, scantily clad blond who requests the victim's assistance in disrobing her. In this particular scam, which is assisted by a piece of malware anti-virus firm TrendMicro identifies as TROJ_CAPTCHAR.A, an additional article of clothing comes off each time the user helps her solve a CAPTCHA.

CAPTCHAs, or "Completely Automated Public Turing test to tell Computers and Humans Apart," are those squiggly agglomerations of letters and numbers that free Webmail providers such as Yahoo! require the user to interpret and input before being allowed to open a new e-mail account. The Webmail providers use the CAPTCHAs to stop spammers and other bad guys from using automated processes to create hundreds or thousands of fake accounts. Those new accounts, of course, are not logged yet by anti-spam filters, so they give spammers a new platform to deliver their garbage.

The images served by the "Melissa" malware are real CAPTCHAs generated by Yahoo!'s Webmail registration process. As a result, each time a victim removes another article of clothing from her, spammers responsible for distributing the malware are able to create yet another Yahoo! account.

According to TrendMicro, the program that generates Melissa is downloaded onto a user's computer by other malware -- a bot or another bundle of adware/spyware. This malware is completely unrelated to the infamous Melissa worm of 1999.

The tactic employed by Melissa, while fascinating, is hardly new. A few months back, I learned of similar activity from security experts at BitDefender, an anti-virus company based in Romania.

BitDefender had spotted a piece of malware it labeled "Trojan.Spammer.HotLan," which apparently succeeded through similar methods of solving between 400 to 500 CAPTCHA requests per hour, solutions that were then forwarded from Hotmail, Gmail, and Yahoo! to facilitate new Webmail account creations.

By Brian Krebs  |  October 30, 2007; 10:20 AM ET
Categories:  Fraud , From the Bunker , Safety Tips , Web Fraud 2.0  
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