Two anti-spam systems developed by Microsoft for Hotmail designed to help ISPs track down offending users were abused by spammers, a lawsuit brought last week by the software giant alleges. The spammers are accused of attacking Hotmail's Junk Mail Reporting Program and Smart Network Data Services to try to prevent the mail service from classifying messages correctly.

The suit, Microsoft Corporation v. Boris Mizhen, et al., claims that the defendants created millions of Hotmail accounts and used them to falsely label up to 200,000 spam messages a day as legitimate mail. With this evidence of "legitimacy," an associate of Mizhen then contacted Microsoft asking that the company stop treating them as spam. Microsoft asserts that this deception allowed Mizhen and his affiliates to disseminate a "vast quantity" of spam to Hotmail users, and that this violates various federal laws including the CAN-SPAM act.

This is not the first time that Boris Mizhen has been sued by Microsoft. He was sued in 2003 for spamming Hotmail users; the case was settled, with Mizhen agreeing to pay the company $2 million and refrain from further spamming Hotmail users.