It is currently only available via Software Update (which will bring up the Mac App Store in OS X Mountain Lion) not via “Check for Updates” in iTunes 10.7.
The update weighs in at 198 MB.
For information about the security content of this update, visit: support.apple.com/kb/HT1222.
MacDailyNews Take: Schnappy!
[Thanks to MacDailyNews readers too numerous to mention individually for the heads up.]