Malware definitions check and update

To see when your malware definitions were updated, run this from terminal:

defaults read /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/XProtect.meta LastModification

Output is something like:

Tue, 09 Aug 2011 02:44:18 GMT

To force update, run this from terminal:

sudo /usr/libexec/XProtectUpdater