Unraveling security features such as the BitLocker drive encryption, Windows Defender and Windows Security Center from Vista at this late date would be a monumental task, however.

"I can't even speculate on how we'd deal with a request like that," Toulouse said, although he didn't rule out delays in the global release of Vista.

Todd rejected the idea that the EC would give a "green light" to any particular version of Vista, but said that Microsoft would have to produce a product that complies with EU competition rules, or risk an antitrust ruling from the Commission.

"We've made it clear to (Microsoft) for some time that it's up to Microsoft to make products that are fully compliant with EU competition rules, particularly in light of the March 2004 ruling on its abuse of its dominant market position," Todd said.

NeelieKroes, the European Commission's competition commissioner, wrote to Microsoft CEO Steve Ballmer in March to express concerns about the security features and requesting more information on them, but the company delayed responding to the letter until the end of August, Todd said.