Well, according to this News.com story, the outcome isn't pretty: "Windows patch backfires on the security-minded." Here's the deal... Microsoft released a patch last week to fix serious Windows vulnerabilities that could be exploited for a malicious worm attack. Some security-conscious users, who had previously tightened down their access lists, immediately installed the patch. Unfortunately, their proactivity came back to bite them in the butt.
"Microsoft has acknowledged that a patch released last week can cause trouble for some users [those who have changed the default permission settings in order to increase the security of their systems]. It could lock them out of their PC, prevent the Windows Firewall from starting, block certain applications from running or installing, and empty the network connections folder, among other things."
Johannes Ullrich, the chief research officer at the SANS Institute summed it up perfectly when he said that the flawed update delivered "two strikes against good security... First, you get penalized for running an enhanced security template. Next, you get penalized for patching quickly." Microsoft, surprisingly, had no immediate comment.