Change of Stats
If you change your stats, you will NOT be able to connect to online games.
You will be removed from the public leaderboard and will be roll-backed to level 1.
(This is taken from PS3/Xbox 360 notes, so this might NOT apply to PC!)
External Programs
Usage of SOME external programs can cause a ban!
Some have been banned for using external crosshairs.
Regarding to VAC
VAC is loaded on Multiplayer and Zombies, but not on Campaign. Keep in mind this does not mean it is safe to hack on MP or Zombies because of they all have their own anti-cheat running too.
Not Confirmed Notes
Texture Hacking/Modding is against the rules, so this can cause a ban.
Campaign is secure to hack in.
Other Notes
* They have a team of people who work to ban people. (Like BanCandy was in MW3)
So, you never know if you are being watched by they Anti-Cheat Team.
* They are using a server-sided anti-cheat system, called "TAC" (Treyarch Anti-Cheat).
* Your games get's recorded, so if you are to hack. It's easy to prove that you did.
So, that is mostly like what the Anti-Cheat Team will work with along with reports from players.
(So, be aware of your actions! I haven't seen any notes about the option to deactivate it)