Problems in Windows Explorer/ Windows shell due to 908531
On April 11, Microsoft released a security update via Automatic Updates & Windows / Microsoft Update to fix some security issues.
This update applies to Win2000, SBS systems, Win XP, and Windows Server 2003.
Subsequent to this fix, many users have reported various problems in Windows Explorer and also with Internet Explorer, as well as other programs & functions. Many examples can be seen in the MS public newsgroups (and likely elsewhere).
This post, at AumHa Forums, has a list of reported problems, and suggestions on how to resolve them.