Yesterday Microsoft announced an important security vulnerability with ASP.NET.
Since then we have run the auditing script recommended by Microsoft on our hosting servers. All Site Foundation Framework websites pass by default, so all of our website customers can rest assured that their sites are safe from this exploit.
26/09/2010 EDIT: Scott Guthrie has posted an update containing more details. Read it here.
28/09/2010 EDIT: Microsoft has a security update coming to address the issue tomorrow.
Link: Important: ASP.NET Security Vulnerability
Link: ASP.NET Security Update Shipping Tuesday, Sept 28th