Just recently Modern Warfare 2 has been updated via Steam. The patch improves the IWNEt matchmaking. Possible bug fixes and wallhack preventions are not mentioned though.

Along with three new playlists for Modern Warfare 2, Infinity Ward has released a new update adjusting IWNet matchmaking system.

New patch is available through Steam but there´s no detailed description for the patch so we don´t know is it just one fix or a host of several summed up into a statement in the change log.

Anyway, you´ll need to restart Steam client in order to apply the patch.