The European Union's (EU's) warning about Vista might just be the best news about Vista that Microsoft has gotten in a long time. I mean, think about it: If Vista weren't so impressive and comprehensive, why would the EU care so much about it?

In a recent letter to Microsoft, the EU's top antitrust regulator, Neelie Kroes, warns that the software giant won't be allowed to sell Vista in Europe if the OS bundles certain features. Although the exact feature set the EU is concerned about is currently unknown, an EU spokesperson said that the EU specifically mentioned Internet search features, Microsoft Internet Explorer (IE) 7, Digital Rights Management (DRM) technologies, and Microsoft's new Metro feature, which will compete with Adobe Acrobat PDF.

All these features have one thing in common, the EU says: They're currently available from Microsoft or other companies. The fear is that Microsoft will again bundle technologies in Windows in a bid to harm competition.

"We expect that Microsoft will design Vista in a way which is in line with the European competition laws," Kroes said this week. "It would be rather stupid to design something that is not."

The EU is also worried that Microsoft might bundle various security technologies in Vista. Although it didn't specifically mention Vista's Windows Defender application, the EU is concerned because the bundling of such applications might harm third-party developers such as Symantec and McAfee, who make competing products.

Acknowledging receipt of the letter last week, a Microsoft spokesperson said that the company was aligned with the EU's expectations. "Consumers are demanding a more secure, functional operating system," he said. "And Microsoft has developed Vista to respond to that demand, while respecting its legal responsibilities." The EU is currently determining whether to launch a formal investigation of Vista to halt its sale in early 2007.

In related news, Microsoft is allegedly so nervous about its current EU antitrust woes that it hired several former EU justices to stage a mock trial designed to predict how its actual EU court case might proceed. The mock trial was held in January, but there's no word yet whether Microsoft prevailed. Microsoft faces the real thing Thursday and Friday, when it faces off against EU regulators in a closed-door session in Brussels.