Starting today, anyone still making use of Windows 7 Beta will find their operating system shutting down every two hours. Having such a “kill switch” built into the OS likely will cause privacy advocate and others to voice concerns, but for a beta release of Windows it is certainly an understandable move.
Windows already has a tough rep to beat in terms of security, with a lack of prompt updates being one of the most common causes of a compromised Windows machine. Microsoft clearly doesn't want old copies of a pre-release Windows 7 on the Internet. If you still happen to be using the beta, there's no better time than now to upgrade to the RC, which will remain active for another year.