The technique, dubbed "rearm" as a nod to the command used in Windows, can be used up to five times. If users perform the rearm at the end of each 30-day period, they can run Office 2010 for a total of 180 days without having to supply an activation key.

According to a Microsoft spokeswoman, who replied to questions via e-mail, the rearm feature is aimed at enterprise administrators who use a single copy, or "image," to deploy a supported operating system and accompanying software on hundreds or thousands of PCs.

As IT administrators prepare the image, however, the activation clock continues to tick down. By the time the image is copied to a company machine, the counter may have reached the point where the activation messages appear.

"Say you have another 500 computers you want to deploy six months from now," the Microsoft spokeswoman said. "You want to use the same image [as before]. The problem here is that Office is smart enough to know that you [first] installed Office in May, but now it's November. So when users first boot up Office, they see the red title bar telling them they haven't activated. This is not a good user experience."

Rearm lets administrators build the image, then as a final step, reset the activation grace timer. "Now, whenever the administrator has new computers coming in, he can just deploy that image. When users start Office for the first time, the grace timer begins, and users have 25 days before they get a dialog telling them they're not activated."