An erroneous wildcard : Google explains all
Well, such is the devastating power of the wildcard...
Google has provided an official explanation...
http://googleblog.blogspot.com/2009/01/this-site-may-harm-your-computer-on.html
It seems that their update file of malware-suspected sites contained a wildcard typo, a "/" that effectively meant "everything"! Human error, easily overlooked, I guess....