I've been playing cod3 ever since it came out back in 2006. I don't play the ranked matches. Just the regular online multi player. When I started playing, naturally I was horrible, but over the years I've developed into a skilled player more or less.
I don't know if this split screen cheat has been going on way back when, but it wasn't untill a little while ago when I was playing capture the flag. There was one player on the opposite team who managed to sneak up on me and my teammates no matter where on the map we hid. I got suspicious and saw that indeed he had one guy on our team. He was "gamertag" on his team, but on our team he was "gamertag (1)". So he was using his second account just so that he could have our compass as well as eavesdrop on our in game voice. Indeed, his cheating helped his team pull way ahead of us. I called him out over my headset. Telling him that I was aware of his cheating. It was then he quit the game. When he left, my team finally had a fair fight on our hands and we were closing the gap when more people joined the game, only mostly the other side. Out numbering us and preventing us from winning.
Ever since that game, I've become more aware of these cheating split screeners and how they're infecting more and more games. I hate team killers and glitchers, but split screeners are the absolute worst. I cam still fight against team killers and glitchers, but when my team is up against a split screener, forget about it. The team with the split screener will win 99.9% of the time.
The split screener is the guy (sometimes more than one guy as some work on teams) who gets somewhere around 150 points but died only about 12 times. And I've noticed the same gamertags constantly get those high kill scores and low death points. No one is that skilled.