can a flashed 360 still play regular Xbox 360 games online?

i was arguing with my friend that they can still tell if you have a flashed 360 even if you are playing original 360 games online

he insists that that the only way you can get caught is if you play burnt games online that aren’t patched right or something, but that if you play a normal game online that Microsoft will just think its a normal 360

which one of us is right??

They can detect a flashed Xbox 360 regardless if the game. When COD MW2 came out they caught like 200,000 people with illegal copies and permanently banned them from live.