The data contained in the packet will probably contain code for determining the game status (position of players, ammunition, shots fired etc.) and only make sense to the game's program code. No need to ecrypt this info as it is just numbers and make no sense to immortal souls such as ourselves. Some really really clever hacker may take the time to reverse-engineer the games' program code, but "clever" and "hacker" rarely go together. There are a few cases known where it was done however.
Example:
http://www.multicfs.com/project.asp?project=6