C:\Documents and Settings\All Users\Application Data\Microsoft\Microsoft Antimalware\Scans\History\Results
Doing "Properties" for the directory got me the following.
Size: 4.59 GB (4.937,111,896 bytes)
Size on disk: 5.43 GB (5.836,144,640 bytes)
Contains: 603,044 files, 0 folder
That's right. Somebody at MS thought it was a good idea to put over half a *million* 8k files in a *single* directory.