A mistake by Microsoft sent some users into a panic when they received an e-mail that told them their copies of Windows 7 beta would automatically begin rebooting every two hours starting June 1.

Windows 7 beta, which was released to the public in January, will expire on Aug. 1. A month before that, the operating system will prod users to move on to the next milestone, dubbed "RC" for Release Candidate, or revert to an older OS such as Vista or XP. Microsoft doesn't go for subtlety: It warns users of an approaching expiration date by automatically shutting down, then restarting, the PC every two hours.

Although the company had earlier pegged the beta's auto-shutdown as starting on July 1 -- a full month before it expires -- an e-mail it sent to the millions who downloaded the test version used the wrong date.

"We're sending this mail to remind you that Windows 7 Release candidate is available and to make sure you plan ahead for when the Beta expires on August 1, 2009," Microsoft said in a message dated May 24 that was received by a Computerworld reporter. "On June 1, 2009, the PC you're using to test the Beta will begin shutting down every two hours."

The looming deadline and short warning raised hackles. "From the e-mail I just received, it looks like the 'two hour shutdowns' was moved up a month for the BETA," said a user identified as "brxndxn" on the Windows 7 support forum. "And I get a ONE WEEK NOTICE??! And the current FAQ isn't even changed?? How am I supposed to plan around this?"

Others on the same thread, however, accepted the switch, saying it was part and parcel of testing previews. "Beta testing is like that. Unexpected things happen," said "derosnec."

Microsoft caught its error and followed up the original message with another. Computerworld received it Wednesday, May 27. "Because you signed up to test the Windows 7 Beta, we recently sent you mail about the expiration dates for the Beta and Release Candidate. Unfortunately, we made a mistake," read the new message. "We said the Beta would start shutting down every two hours on June 1, 2009. The correct date is July 1, 2009. We apologize for the error and any confusion it may have caused."

Windows 7 RC, unveiled earlier this month to the public, has a June 1, 2010 expiration date, with the every-two-hour auto-shutdowns starting March 1, 2010.

Users can download Windows 7 RC from the Microsoft site through at least the end of July.