Microsoft put out a release day before yesterday (8/13/13) to fix a security vulnerability in ADFS 2.0
It caused an outage for SSO with Office365 for a customer of ours (they had the servers set to auto update).
At the moment we recommend NOT installing these updates.
We saw the following error repeated for every authentication attempt:
Event ID 111 Federation service encountered an error while processing the ws-trust request.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation ---> System.TypeLoadException: Could not load type 'Microsoft.IdentityModel.Protocols.XmlSignature.AsymmetricSignatureOperatorsDelegate' from assembly 'Microsoft.IdentityModel, Version=220.127.116.11
It goes on with the stack trace.
Uninstalling these updates has partially restored service: Outlook and Lync now work, but the Outlook Web Access and SharePoint online still aren't working.
In fact they pulled the patch later in the day yesterday.