The Microsoft Corp. confirmed late last week that a security patch released by the company could in fact wreak havoc on the user's machine by shutting down the firewall, preventing the applications from running or locking the user out entirely.
The patch was released to fix four critical flaws in Windows Server 2003, Windows XP and Windows 2000. It was released after experts said that one of the four flaws could be exploited by particular worm over the next few weeks.
The patch can only cause problems when the default permission settings in a Windows directory have been manually changed. Microsoft have released a guide to help users reset the permission settings. Source