[Acutulus]

I remember playing a first person shooter called Red Faction on PC maybe 15 years ago. Through some poking around I (and many others) discovered that when a client joined a multiplayer game, the server would instruct each client to load a large .dat file local to the client containing presumably a bunch of global assets. Within that were numerous object, physics and game state variables in plain text ripe for the picking. The server would proceed to accept any .dat file that contained the necessary declarations regardless of their value.

I recall seeing players hovering in the air and spinning while shooting rockets out at hundreds of rounds a second. There was also a way to modify your files such that you could crash a game just by joining it. The experience was as interesting and fun as it was awful.