VAC banned accounts can still play single-player games, local LAN games, and multiplayer on non VAC-secured game servers. To find non VAC-secured servers, from the Steam main menu click on View, select Servers, then select Not secure in the Anti-cheat dropdown.
Cheating in one of the following Source games or a Source mod will result in a VAC ban for all games in the list below:
Half-Life 2: Deathmatch
Day of Defeat: Source
Team Fortress 2
Similarly, cheating in one of the following Gold Source games will result in a VAC ban for all games in the list below:
Day of Defeat
Team Fortress Classic