Soft-core porn site Perfect 10 is suing Microsoft, claiming that the MSN search engine is providing links and images to sites that are illegally hosting its content.

Microsoft is not the company's first target, as it recently lost similar cases against Google, Amazon and A9 search, all of which it is appealing.

The suit was filed on Tuesday in a California district court and alleges that the MSN image search engine creates unauthorised thumbnails of Perfect 10's premium content, as well as including links to see full-size versions of the images for free.

The complaint also claims that the search engine is finding passwords to its paid-for content on other sites, thereby allowing it to access Perfect 10's pay-only material, and that Microsoft is receiving money through advertising from websites that are illegally hosting the images.

"Microsoft has rejected efforts to reach a settlement and our business is being destroyed," said Norm Zada, president of Perfect 10.

Zada claims the search engines are responsible as they make it easy for surfers to find infringing content, and is costing the company $4m a month.

Perfect 10 initially attempted to sue several sites that it says were stealing its content, but "it's absolutely hopeless. A lot of these people are in Russia or China," said Zada.

At one point it looked like Perfect 10 might win its case against Google and Amazon when a judge ruled that they could be partially liable for infringement for displaying the thumbnails.

However, a judge for the Ninth Circuit Court of Appeals later overturned that decision citing "fair-use" principles and pointing out that the full-sized images were not hosted by the search engines.

Perfect 10 is appealing the court overruling, but as yet no court date has been set.