canonicalization issues with ASP.NET
Brian just post an announcement on the www.ASP.NET regarding the authentication / canonicalization issue with ASP.NET, so.. use UrlScan, and pay attention to the Global.asax now.. now!
MS KB: http://support.microsoft.com/?kbid=887459
More Info: http://www.microsoft.com/security/incident/aspnet.mspx
Colt Kwong