April 2004: Windows 2000 bricked
In April 2004, Microsoft sent a slew of patches down the automatic update chute, one of which (MS04-014) locked up a sizable percentage of all Windows 2000 machines. That patch was supposed to fix a hole in the Jet Database Engine.
Knowledge Base article 841382 tells the tale:
[Y]ou may experience any one of the following symptoms:
• Your computer appears to stop responding at startup.
• You cannot log on to Windows.
• Your CPU usage for the System process approaches 100 percent.
The company sure plugged that one.