See if this will work for you
Click on the start button
click on All Programs locate Microsoft Security Essentials, click on the "Settings" tab. Select "Excluded files and locations"
Browse to "C:\Program Files (x86)\Microsoft Security Client\MsMpEng.exe", click on Ok and press Add button to add the file to your list of excluded files and locations. Press Save changes button.
In Windows 7 x64 . You will have two Program Files folders . Program Files is where 64-bit applications install to and Program Files (x86) yes you guessed it 32-but applications install to .