Microsoft Security Bulletin MS08-067 – Critical: Vulnerability in Server Service Could Allow Remote Code Execution (958644)
Let's make it simple: PATCH NOW. Microsoft's say that this can spread from machine to machine without authentication, and reliable exploit code is likely. This makes it the ideal security flaw to hook a worm onto, like Blaster or Sasser.
If you're a corporate user with a firewall DO NOT imagine that the firewall will offer you much in the way of protection. Eventually either a worm-infected laptop will be plugged into your internal network, or possibly a infected machine may breach the firewall when it connects through the VPN. If there is a widespread outbreak and you're not prepared, then shutting off your VPN may buy you some time.