According to an email from a Microsoft employee to a large Vista distributor, Microsoft has flipped a switch that will begin disabling copies of Vista they decide are not genuine:

Good afternoon, as of this week, Microsoft has activated a function in Vista called ‘Reduced Functionality.’ This is a specific function in Vista that effectively disables nongenuine copies of Windows. Therefore anyone who has a pirated copy of Vista will experience:

A black screen after one hour of browsing
No start menu or task bar
No desktop

Please communicate this antipiracy initiative from Microsoft to your resellers — note this function has only just been activated in Vista worldwide and therefore any issues with nongenuine versions will start to arise from now onward.”

Lets hope Microsoft can keep their authentication servers working.

UPDATE: Nope, it’s a hoax:

Microsoft was quick to debunk this e-mail warning of a Black Screen of Death. A Microsoft representative told Wired News “the reporter received inaccurate information,” and that the company has not rolled out any updates to Windows Vista’s anti-piracy platform.