"This is a pre-authentication, remote code bug," said Andrew Storms, director of security operations at nCircle Security, referring to MS12-020, the one critical bulletin today and the update that he, other researchers and even Microsoft urged users to patch as soon as possible.

"It will allow network execution without any authentication, and has all the ingredients for a class worm," said Storms.

"I'm particular spooked by this one," said Jason Miller, manager of research and development at VMware. "Hackers want [vulnerabilities] that don't require authentication and are in a part of Windows that's widely used. I guarantee that attackers are going to look at this closely."

patches a pair of bugs in Windows' Remote Desktop Protocol (RDP), a component that lets users remotely access a PC or server. RDP is frequently used by corporate help desks, off-site users and IT administrators to manage servers at company data centers and those the enterprise farms out to cloud-based service providers like Amazon and Microsoft.

The critical vulnerability, dubbed CVE-2012-0002, could be exploited by an attacker who simply sends specially-crafted data packets to a system with RDP enabled, said Microsoft.