For Exchange Server 2010, the Standard CAL spam definition updates’ll become available over the next couple of days and will be published twice a month from that point on. Exchange Server 2010 Enterprise CAL anti-spam definition updates will not be provided by Microsoft Update. They’ll be made available via Forefront Security for Exchange.
For WSUS administrators, you may notice previous Product Classification "Exchange Server 2007 Anti-spam" is now "Exchange Server 2007 and Above Anti-spam".

Full Article: Exchange blog