Microsoft has sued a Hong Kong seller of mobile ringtones, saying the company used phishing techniques to flood Microsoft Live Messenger users with spam messages.

The lawsuit accuses a company called Funmobile of sending out thousands of spam instant messages over the past four months. The case was filed last month in King County Superior Court in Seattle, but Microsoft did not name the company involved until Thursday. Microsoft is seeking a court injunction to stop the spam, as well as monetary damages.

According to court filings, Funmobile and its US subsidiary, Mobilefundster, have sent out instant messages that included links to phishing sites controlled by the company. Victims who clicked on a link would sometimes see a website - called MeetYourIM - that asked them to enter their MSN email and password so they could participate in a "Harmless community site which is offering users a platform to meet each other for free."

If the victim entered his credentials, Funmobile would then harvest all of his friend's addresses and then spam them, Microsoft said. This kind of spam - also known as spim - is particularly effective because it looks like it's coming from a friend.

"This kind of activity crosses the line from legitimate third party services to 'parasiteware' that harms our customers," wrote Tim Cranton, a lawyer with Microsoft's Internet Safety Enforcement group, in a blog posting.

Windows Live users should "never disclose their Windows Live ID and password to a third party other than Microsoft", Cranton said.

Funmobile is run by brothers Christian and Henrick Heilesen, according to court filings. The company did not respond to messages seeking comment.

About 320 million people use the Windows Live Messenger system.