Microsoft Corp. said it has filed three lawsuits against “cybersquatters,” in an effort to fight back against a surge of online trademark infringement by people seeking profit from pay-per-click advertising.

The Redmond, Wash., software giant said cybersquatters and typosquatters — people who register Web addresses either with trademarked terms or with common misspellings in the hopes of luring Web surfers who mistype addresses into their browsers — are now registering more than 2,000 domains each day targeting Microsoft.