April 2006: The pretax predicament
On the April 2006 Black Tuesday, Microsoft released MS06-015, a patch for Windows Explorer. By the weekend, most Windows users with auto updates turned on got it -- right across the face. The weekend before tax day, many Windows customers found they couldn't navigate to the Documents or Pictures folder, couldn't open or save files, had to type http:// into Internet Explorer to keep it from freezing, and much more.
We ultimately discovered that the patch messed up any machine with an older HP scanner program or an older Nvidia video driver.
Microsoft's ultimate workaround (KB 918165) included a manual fix procedure that any computer-science grad would be proud to explain, if they can figure it out.