Download the latest Virus Defs from here:

http://go.microsoft.com/fwlink/?LinkID=121721&clcid=0x409&arch=x64

Make sure the file is called: "mpam-fex64.exe" for 64bit computers

md d:\offline
Dism /Mount-Image /ImageFile:D:\offlinedefender.wim /index:1 /MountDir:d:\offline
copy mpam-fex64.exe to D:\Offline\Program Files\Microsoft Security Client and to d:\offline
Dism /Unmount-Image /MountDir:C:\test\offline /commit

If needed Import and replace the WIM in the boot folder on the WDS server.