Hi,
Thank you for the post.
Generally speaking, Forefront Client Security is powerful security production. It not only delivers unified protection from viruses, spyware, and other malware threats, it also adds significant value to customers by delivering simplified administration and critical visibility into threats, while easily integrating into the existing environment.
I would recommend you to please update the FCS signature definitions on the client and scan the machines, if the issue still retains, please send the sample of the malware to : https://www.microsoft.com/security/portal/Submission/Submit.aspx. As you know, this is our best way to add detection for the malware that are currently not detected.
Thank you for your understanding.
Regards,
Nick Gu - MSFT