Forefront Security for Office Communications Server can help you protect your Office Communications Server 2007 instant messaging environment against malware and out-of-policy content. Forefront Security for Office Communications Server supports both Office Communications Server 2007 Standard Edition and Office Communications Server 2007 Enterprise Edition, in addition to the latest Office Communications Server 2007 R2 release.

Get it here: http://www.microsoft.com/forefront/serversecurity/ocs/en/us/default.aspx