Miscreants have created a strain of malware capable of setting up bogus Hotmail and Yahoo! accounts in order to send spam.

The HotLan-A Trojan uses automatically-generated webmail accounts, suggesting that spammers have found a way to bypass the Captcha system (which typically means accounts can't be created until a user correctly identifies letters depicted in an image).

The Captcha system was set up by online service providers in order to try to ensure that only requests generated by a human, and not automated by a program, are serviced.

These challenge-response systems are often used to stop the automatic creation of webmail accounts by spammers, so their apparent defeat by the HotLan-A Trojan is of particular note.

The use of compromised PCs to send spam has been going on for years, but the HotLan-A Trojan follows a more complex routine. Each active copy of the Trojan attempts to set up a webmail account before pulling encrypted spam emails from a website. It then decrypts these junk emails and sends them to (presumably valid) addresses taken from yet another website, according to an analysis of the malware by Romanian anti-virus firm BitDefender. Junk mail sent using the malware has largely been used to spamvertise sites flogging pharmacy products.

"There are only about 500 or so new accounts being created every hour," said Viorel Canja, head of BitDefender's Anti-virus Lab. "But still, we've seen 15,000+ Hotmail accounts being used so far. It's hard to estimate how many spam emails have already been sent." ®

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