Since then, Microsoft has taken considerable heat from consumers and the media, who have likened WGA to spyware that has sometimes inaccurately labeled legal copies of Windows as pirated.

Through its spokeswoman, Microsoft said that "80% of all WGA validation failures are due to unauthorized use of leaked or stolen volume license keys."

Still, WGA has been so controversial that it led a French programmer to develop a tool to delete WGA and a Windows customer in Los Angeles to file a class-action lawsuit.

Microsoft has tried to appease customers by releasing a new version of WGA that checks users' computers only once a month, rather than every day.

The lawsuit, filed this week in U.S. District Court in Seattle, alleges that WGA violates antispyware laws by not fully disclosing itself when it was delivered to Windows users through Auto-Update. The suit is headed by the same lawyer who also led the class-action lawsuit earlier this year against Sony Corp. for not disclosing that it had placed copy-protection rootkit software on customers' PCs via music CDs it sold. The rootkits disabled users' protections against viruses and spyware. Sony later settled the lawsuit.