Microsoft today began an anti-spam blitz by filing seven lawsuits against hackers who allegedly used PCs infected with Trojans to send sexually explicit spam email that violated the Can-Spam US anti-spam law.

"Sexually explicit materials and publications for sale in stores are required by law to be covered from view with a brown paper wrapper, and it is important that consumers are protected online in the same way," said Nancy Anderson, vice president and deputy general counsel at Microsoft.

Spam that contains sexually oriented material that is initially viewable in the email violates provisions known as 'brown paper wrapper' in the Can-Spam law and Federal Trade Commission rules.

The labelling provisions require such email solicitations to include the words 'sexually explicit' in both the subject line and the initially viewable area of an email.

The seven lawsuits were filed in Washington State Superior Court in King County against 'John Doe' defendants who have yet to be identified.

The actions allege violations of the Can-Spam federal law and Washington State's Commercial Electronic Mail Act, including using compromised computers around the world to route spam email, using misleading subject lines, and failing to include an unsubscribe option and physical address.

Collectively, defendants in these cases allegedly sent hundreds of thousands of email messages.

"Labelling requirements for spam are important, and the 'brown paper wrapper' rule is a particularly important provision," said Anne Mitchell, president of the Institute for Spam and Internet Public Policy.

Microsoft has now supported over 115 legal actions worldwide against spammers, including filing 86 lawsuits in the US.