Turbo'ing is the act of trying to change to a Gamertag that is about to be swapped or changed onto another account. Usually, this is done with a turbo program. Our rules do say that doing this is not allowed even though there are sales going on everyday on-site regarding them. You could say that's why so many gamertags are turbo'ed now, because just about everybody has one.
No lets say you had the tag Banana, if you were to change the tag and attempt to put banana on a NEW account the program would snatch the gamertag and put the tag on a fresh silver account,
I'd say always if the Gamertag has been released on a thread or somewhere for everyone to see, if you keep it secret like you see many doing now than the chance is really not there.