Using aimbots — or any unauthorized third-party software that modifies game behavior — on Xbox 360 violates the Xbox Live Terms of Service and the game's EULA. Consequences include permanent console bans, account suspension, and in some jurisdictions, legal action under anti-cheat statutes (e.g., DMCA §1201, CFAA).
Fair competition is why multiplayer exists. Invest time in fundamentals — the payoff lasts longer than any cheat.