VAC (Valve Anti-Cheat System) was enabled for Dying Light on the 29th of January 2016.

Dying Light's Online Options should have a section called 'VAC Secure Game'. Enabling this option will separate a game from other games that have the VAC option disabled or from those that are banned.

On the other hand, banned players will still be able to search for and join games with disabled VAC options as well as other banned games.

It is also worth noting that VAC bans have no impact on the single-player campaign.

Players that would like to be protected will simply need to enable the 'VAC Secure Game' option.

Related Terms:

Secure Game - a game that has the 'VAC Secure Game' option enabled and where there are no banned players (including the Host).
Not Secure Game - a game with the ‘VAC Secure Game’ option disabled and where there are no banned players.
Banned Game - a game with at least one banned player - regardless of the ‘VAC Secure Game’ settings.

Secure Games can only look for other Secure Games.
Banned Games and Not Secure Games can look for each other.
Banned players that have switched their Online Options to ‘VAC Secure Game’, will receive a message informing them that they will only search for games among Not Secure Games and Banned Games when entering the Find Games or Quick Join menus.

A Not Secure Game can be invited by a Secure Game and join it. Such a game will maintain a Secure Game status.
A Secure Game can be invited by a Not Secure Game, but before joining, there will appear a message telling you that you are attempting to join a game to which banned players may also be able to join.
With respect to Secure Game to Banned Game invites and vice versa, there will be a message informing you why this connection may not be established.

A Banned Game to a Secure game connection can never be successful, nor can a Secure Game join a Banned Game.
A Banned Game and a Not Secure Game can always join each other.
A Not Secure Game to a Secure Game connection should always work.
A Secure Game to a Not Secure Game connection should be successful only when you expect it, i.e. there is an invitation, while a message informing you that the game will not be protected has been displayed. In all other instances, a Secure Game should not be able to join a Not Secure Game.

Having disconnected from a game, the ‘VAC Secure Game’ option should return to its value from before the connection.

Option settings:
The ‘VAC Secure Game’ settings in the ‘Online Options’ menu can only be changed if your game mode is switched to 'online'.
If you are not in the game's main menu, but instead your level is loaded, then ‘VAC Secure Game’ cannot be additionally modified in single-player parts of the game as well as when you are connected with another player.