Its free! And works great. So if you do not run virus protection in your Organization, grab and it start!
Download URL for client: http://windows.microsoft.com/en-us/windows/security-essentials-download
Silent install for client:
start /w "" "%~dp0mseinstall.exe" /s /runwgacheck /o
Download URL for definition updates for Microsoft Security Essentials: http://support.microsoft.com/kb/971606
Silent install for definition updates for Microsoft Security Essentials:
start /w "" "%~dp0mpam-fe.exe" /s
Download for latest Network Inspection System Definition Updates:
X86: http://definitionupdates.microsoft.com/download/definitionupdates/x86/nis_full.exe
X64: http://definitionupdates.microsoft.com/download/definitionupdates/amd64/nis_full.exe
Silent install for Network Inspection System Definition Updates:
start /w "" "%~dp0nis_full.exe" /s
/Brian G