A Microsoft spokeswoman declined to say how often OGA is wrong. But on its tech support Web site, Microsoft says that OGA can fail to validate a legitimate copy of Office XP or 2003 for a number of reasons, including if the PC's time is off by more than 24 hours, or if the registry is modified or damaged -- something that can be caused by a virus or spyware.

Microsoft declined to specify if and when it plans to make OGA mandatory. It is being tested with users now in eight languages, including English.

"We are absolutely committed to having Microsoft Office participate in the advantages of Microsoft's overarching Genuine Software Initiative but have nothing further to discuss at this time as the program has not launched worldwide," a spokeswoman said in e-mail. So far, OGA has resulted in few complaints.

"If in the future OGA is kept like this, then that's OK for me," said Guillaume Kaddouch, a French programmer whose free tool for removing WGA has been downloaded half a million times. Kaddouch said he has no plans to write a tool to remove OGA.

While some suggested that Microsoft has learned its lesson with the WGA brouhaha, others said Microsoft is unlikely to abandon the Genuine Software Initiative because it is central to the company's evolving software-distribution model.