Ok, this isnt really a hack, its more of a glitch, but anyway, here ya go...
This is what you need:
1. Two computers
2. Two registered crossfire accounts.
Heres what to do:
1. Log on to your main acc. on one computer, and login to your other acc. on your other computer.
2. Go to a low traffic server/channel, and create a room with a password.
3. Join the room so that both accounts are in the same room.
4. Set time limit/kills to whatever you want, doesnt really matter.
5. Start the game, and kill your second account with your main until time limit/score limit is reached.
NOTE: DO NOT over use this. This is meant to be used to boost your K/D, so use it about once a month or so. Dont go doin this shit for hours straight. We dont want this shit to get patched like it did in CA.