A new product family called Antigen will be added to WSUS server in next few days, says Microsoft. The Antigen product category will include updates, including service packs, optional updates, and critical or security updates, for the Microsoft Antigen 9 for Exchange and Microsoft Antigen 9 for SMTP. Antigen product updates are going to be offered through Microsoft Update and WSUS. Updates offered through this category will apply only to computers running Antigen 9 for Exchange and SMTP with Service Pack 1 version or later.
More info: Microsoft Antigen