Playstation 3: Call of Duty 4: Modern Warfare Question?

Has anyone else notice that there is hacking activity in Call of Duty for PS3, I was just playing a game of Team Deathmatch on the map Countdown and There was a Sniper who was in the woods area and you could barely see him, Is there anyway to stop this, I quit games like Soldier Front and Gunz from ijji (crappy games) and there were hacks there and I thought its impossible to hack on the PS3, So I went there and BAM! A hacker with unlimited ammo and who was right in my base when my game started and slaughtered everyone in my team. Anyway we can contain and or stop this, I don't want to quit the ps3 or Modern Warfare because of Ignorant little punk ruining the game for me. Put Your thought on the bottom