Microsoft will feed Windows Vista users an update in the next week to finger illegal copies installed with cracks that the company will bust when it rolls out Service Pack 1 (SP1) next month.

The just-announced update, which will go out via Windows Update (WU) and install automatically on most Vista machines, will detect two cracks commonly used to activate pirated copies of the operating system. The cracks evade Vista's built-in counterfeit-detection technology by sidestepping product activation and spoofing a legitimate installation.

One of the cracks, "Grace Timer," extends Vista's activation grace period, which is normally 30 days, until the year 2099. The other, called OEM BIOS, modifies system files and the PC's BIOS to mimic the product activation done by computer-makers at the factory.

Both will be blocked by Vista SP1, the major update that will hit WU as an optional download in mid-March and automatically download and install the next month.

February's Vista update, however, will only detect cracks, notify the user and offer up a solution, said Alex Kochis, senior product manager for Microsoft's Windows Genuine Advantage program, in a post to the team's blog. It will not disable, block or cripple the cracks.

"It's important to note that this update does not disable the exploits it finds," said Kochis. "It simply alerts customers that exploits exist." At the same time it rolls out the crack-detection update, Microsoft will also post a separate removal tool for download, Kochis added. "In the future, we will integrate the removal of the exploits with the detection," he said.

If the crack sniffer detects an activation hack, it will pop up a warning that includes a link to the removal tool. People whose PCs don't have Grace Timer or OEM BIOS on their PCs will not see the pop-up.

Kochis also detailed what happens when users upgrade to SP1 if they take no action after being told a crack has been found. People who used Grace Timer to scam the system will start seeing Vista's new dunning messages immediately, he said; those who relied on OEM BIOS will begin receiving the alerts about 15 days later.

Currently, Vista SP1 is in limbo, since Microsoft yanked a prerequisite update -- not associated with the crack-detection add-on that Kochis touted -- from distribution after users reported it sent their PCs into an endless loop of reboots. That update must be in place before Microsoft can send SP1 to users via Windows Update.

Today, a company spokeswoman said that the snafu would not delay SP1's March debut. "This will not affect the SP1 release schedule," the spokeswoman said in an e-mail. "We are on schedule to release Windows Vista SP1 to Windows Update and the download center in mid-March and to users using Automatic Update in mid-April."