The Redmond, Wash., software maker filed the claims Thursday in Washington state court against five unknown individuals under the business names Soft Solutions, DirectAd, qiweroqw.com, ITmeter INC. and ote2008.info.

Microsoft's associate general counsel, Tim Cranton, announced the move in a blog post.

The company is accusing the defendants of spreading so-called "malvertisements," ads that can end up infecting computers with damaging software.