Microsoft no longer provides updates for the Norman Data Defense antivirus engine that's used in Microsoft Forefront Protection. This includes Forefront Protection for Exchange, Forefront Protection for SharePoint, and Forefront Security for Office Communications Server.
The engine licensing contract between Norman Data Defense and Microsoft has expired. Because the majority of the Forefront Protection product family is set to reach an end-of-life state at the end of 2015, Microsoft isn't extending the Norman engine license.
For continued protection, use the remaining suite of antivirus engines that are provided in Forefront Protection.