Why would they care about that? People can go in achievements servers, screw up their stats and get the achievements with relatively small efforts, or just use this.
Granted its a hack, but its not even used when anyone is here since you use it in the menu (thus, VAC is not looking for hacks, and no one else can be affected).
Another point, Valve will not do anything against anyone getting their achievements non legit way. Since they caused absolutely nothing to any other players in any way, they would be shooting themselves in the foot by loosing more players.
Although they could fix it eventually and "that" would be in their interest, no one can get banned for such little thing.
Confirming that this indeed does work for the new Heavy Achievements, so definitely hang on to it for all the new achievements that will be coming out.
you dont even need to run TF2 to unlock the achievements, just installed, it cant be detected because its a actual memory hack and valves anti cheat system only works if you actually use a hack that injects itself into the actual game, the only way you could possibly get banned for this is if you used it like 5 minutes after the achievements came out and one of the achievements had something that would take AGES to get (IE : Pyromancer, 1,000,000 Damage) and even then... 1 in a million chance
There's no point in getting the achievements if you're just going to use a hack to get them. The whole point of them is that they're something fun to do.
Linear Mode
