Like its predecessor, Windows 7 can be used for up to 120 days without providing a product activation key, Microsoft confirmed today. Although Microsoft generally touts a 30-day time limit for users to activate their copies of the company's operating system, a little-known command designed for corporate administrators can be used by anyone to "reset" the countdown up to three times.

Late yesterday, the Windows Secrets newsletter published step-by-step instructions on using a single-line command to add an additional 90 days to the stock 30-day grace period.

Microsoft allows users to install and run any version of Windows 7 for up to 30 days without requiring a product activation key, a 25-character alphanumeric string that proves the copy is legitimate. During the 30-day grace period, Windows 7 operates as if it has been activated. As the grace period shrinks, however, increasingly-frequent messages appear on the screen. For example, on days four through 27, a pop-up asks the user to activate once each day. During days 28 and 29, the pop-up displays every four hours, while on Day 30, it appears hourly.

But by invoking the "slmgr -rearm" command at a Windows 7 command prompt, users can reset the time-until-activation to 30 days, said Woody Leonard, a contributing editor to Windows Secrets and the author of several computer books, including Windows Vista All-in-One Desk Reference for Dummies.

"You can run the -rearm trick a total of three times," said Leonard. "If you perform a -rearm at the end of each 30-day period, you end up with 120 days of full, unfettered Windows 7 use, without having to supply an activation key."

Leonard tested the command on Windows 7 RTM (release to manufacturing), the final build of the operating system that Microsoft has already shipped to computer makers and distributed to IT professionals and developers who subscribe to the TechNet and MSDN services.

Microsoft confirmed that "-rearm" can be used as many as three times by Windows 7 users to avoid activation. "This means [that] a total of 120 days total time is available as a grace period to customers that take advantage of -rearm," said a company spokeswoman.

Read the entire article at ComputerWorld.