Microsoft claims updates sent out to Windows XP and Vista machines without users knowing about them were for the Windows Update mechanism, though the company acknowledged it could have been more "transparent" before changing files on user computers.

The company's response came after users expressed concern over updates to XP and Vista machines that were pushed out even when they had turned off the automatic updating feature of Windows Update. The updates were noted as "secret updates" in published reports and on user forums, and Windows users expressed concern that Microsoft would update their computer files without their knowledge or consent

Microsoft regularly pushes out updates to Windows machines but will only update the machine without user action if automatic updating is enabled. If it is not, a user must activate Windows Update to upload an update to the machine.

In an e-mail through its public relations firm Thursday, Microsoft said that the Windows Update service automatically updates itself "from time to time to ensure that it is running the most current technology." "This is normal behavior, and it has worked this way since the service debuted several years ago," the company said.

However, Microsoft acknowledged that it could have better informed users about how Windows Update behaves so as not to spur the confusion that ensued with updates that were sent out last month.

"We could have been clearer on how Windows Update behaves when it updates itself," the company said in its statement. "We've received helpful and important feedback on this point, and we are now looking at the best way to clarify [Windows Update's] behavior to customers so that they can more clearly understand how [it] works."

Despite the recent faux pas, Microsoft still is encouraging users not to turn off the automatic feature of Windows Update, claiming it's the best way to ensure they get critical updates from the vendor, including those that are security-related.