My SBC Yahoo! Virus Protection rejected Microsoft "April 2006, Cumulative
Patch" this AM because it detected the virus 'W32.Swen.A@mm' in the file and
was unable to clean it, so they removed it.
The April 2006 patch? Has it been released yet? "Second Tuesday of each
month" is patch day.
http://www.microsoft.com/technet/security/current.aspx
If you did receive the April patch early through MS channels, check the
info to see if it includes this month's updated Malicious Software Removal
tool. Most likely, your antivirus has produced a false positive. It has
mistakenly read the info that this tool uses to check for that virus as the
actual virus.
If you received the patch some other way than directly through MS, I don't
know what you received. It could be a fake package made to look like it's
from MS.