I'd like to know what messages appear when somebody is cheating and VAC detects it. Do they appear in-game (for games which support VAC natively) or via Steam's game overlay (opened by pressing shift-tab)? Does the game immediately close to show the message? What happens on the screen of the banned player and the players on the same server throughout the whole process?
I couldn't find unmodified screenshots or detailed enough info on google. This post briefly lists the things that trigger a ban, but not how it notifies the user of detected cheating visually.
Best Answer
Caveat: I have never been VAC banned so all information provided below is from different sources across the internet.
When a player on the server is VAC banned
The notification most likely varies slightly from game to game. In Source games, a message will appear in the chat stating something like
You can see this in this screenshot:
Source
(It's fairly blurry sorry, I'm still looking for a better quality picture)
When you are banned
Again, the notification varies slightly from game to game, but if you are VAC-banned mid game, you will get a notification similar to this:
According to the TF2 Wiki, you will recieve the following notification when you try to connect to a VAC-enabled server.
Message displayed to a VAC-banned client.
The TF2 wiki explains in further detail the different measures that take place in the event of a VAC Ban. In addition to receiving the above message:
Needless to say, it would not be a very pleasant situation to be in.
Sources: