An aimbot on halo is basically when you press a key and the program will aim at the person for you, where you can shoot and kill them. It is not that great, and I prefer to play without it, i just got it 5 minutes ago and it is kinda annoying, you have to press the shift key to aim it, and I can pwn myself with it if that was possible, its basically good in NORMAL slayer and CTF Games, like 4 people max. I am playing without it right now, and I only play with it when im bored in small CTF or slayer games. Also note unless the person is a dumbass, aimbot can be easily noticeable.
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Note: Halo Aimbot is not recommended, it will NOT teach you to get better at the game, and I tested it and 70% of the time the bullets
missed. So, I would only use it when you want a laugh, and I recommend using it when there is a 4 player game. You will know the AimBot is working because there will be a flashing '8' in the top left corner of the halo screen.