Companies that use Microsoft's Automatic Updates feature will have to install desktop blockers to thwart the delivery and installation of Windows XP Service Pack 2 this week.

With Microsoft having changed its policy to deliver service packs through Automatic Updates, users that have the mechanism activated now must defend their desktops in order to have time to complete testing.

IT departments are going through rigorous testing, at Microsoft's request, to figure out which applications XP SP2 might break.

IT executives inundated Microsoft with complaints about the automatic upgrades, which forced Microsoft to create an ad hoc team that worked five days to devise a solution. The team came up with a registry key, which prevents Automatic Updates from downloading XP SP2, and a group of three mechanisms for delivering the key to desktops.

Now users have load the registry key onto desktops before Automatic Updates kicks off this week and begins deploying XP SP2.

"It has been confusing in the sense that when Microsoft first announced its intentions of pushing out SP2 to Automatic Updates-enabled computers, it did not announce that it would provide tools to temporarily block delivery of SP2," says Chris Shilt, system administrator for The Relizon Company, a document, marketing and billing service provider in Dayton, Ohio. He has 2,000 desktops with Automatic Updates activated.

"Microsoft should have made the announcement earlier," Shilt says. "The decision to post these tools is a realization that some of their customers are using Automatic Updates to patch systems."

Company officials acknowledge they were caught off guard.

"I was astounded by the number of companies that use [Automatic Updates], which is great," says Barry Goffe, group product manager for Windows product marketing at Microsoft. The company's "Protect Your PC" campaign encourages users to activate Automatic Updates. "Some companies had tens of thousands of machines with [Automatic Updates] turned on."

A recent survey by Web site NTBugTraq shows that 24% of Windows users employ Automatic Updates to get patches.