Government regulators are trying to shut down a company they say secretly downloaded spyware onto the computers of unwitting internet users, rendering them helpless to a flood of pop-up ads, computer crashes and other annoyances.

The Federal Trade Commission accused Walter Rines of Stratham, New Hampshire, and his company, Odysseus Marketing, of luring computer users with the promise of free software that would make peer-to-peer file sharing anonymous. The claim was bogus, the agency said, and the software was bundled with spyware that was secretly downloaded onto computers.

The agency also said the spyware was nearly impossible to remove. Rines, the FTC said, offered his own "uninstall" tool, but it did not work and actually installed additional software.