This is automatic message:

Good day! This account has been flagged as suspicious for violation of the Terms of Service Agreement by Steam Support. Trading on the following account will be permanently disabled in 1 hour.

When the software detects a cheat on a player's system, it will ban them in the future, possibly days or weeks after the original detection. It may kick players from the game if it detects errors in their system's memory or hardware. No information such as date of detection or type of cheat detected is disclosed to the player. After the player is notified, access to online "VAC protected" servers of the game the player cheated in is permanently revoked and additional restrictions are applied to the player's Steam account.

The decision is permanent and it can't be undone.

If I'm VAC banned what does it mean for my account?
Account will be useless. You cannot play on any valve secured server nor trade any items once the ban is implemented.
Note: Users are not Trade banned based on alone reports. Other factors are taken into account before Trade bans are issued.