Some users are newly observing that they are unable to connect to the Call of Duty: Modern Warfare 2 online services recently. It appears that after nearly six months of allowing VAC banned users to play online freely, they are now rejecting them once more.
Writing this today as it was very confusing to figure out for a friend why they were unable to play tonight. They had a VAC ban in the game from six years ago.
Hope this helps, and sorry to be the bearer of bad news!