no, it's not retroactive, but any future game bans and vac bans carry over to prevent ban circumvention

引用自 bRKN：

About STEAM family

if one family member has VAC ban and i get added to his family slot, would i get vac too?

Bans don't share before the cheating infraction occurred. Likewise, previous bans don't share after the infraction occurred and...

https://psteamcommunity.yuanyoumao.com/groups/steamfamilies/discussions/0/7204143093508096647/#c7204143093508110549

引用自 space：

no, it's not retroactive, but any future game bans and vac bans carry over to prevent ban circumvention

Bans only transfer between shared games. If you're playing your own copy of some game with VAC anti-cheat and you cheat in it, your siblings don't get banned unless they also cheat.

引用自 Ben Lubar：

引用自 space：

no, it's not retroactive, but any future game bans and vac bans carry over to prevent ban circumvention

Bans only transfer between shared games. If you're playing your own copy of some game with VAC anti-cheat and you cheat in it, your siblings don't get banned unless they also cheat.

Even if they don't play it, if someone in a Family or shares and email/phone number between accounts cheats all members of the Family or the shared email/number also get a VAC ban for that game, even if the other accounts haven't played it to prevent the use of alts to ban evade.

引用自 Hikari Light：

引用自 Ben Lubar：

Bans only transfer between shared games. If you're playing your own copy of some game with VAC anti-cheat and you cheat in it, your siblings don't get banned unless they also cheat.

Even if they don't play it, if someone in a Family or shares and email/phone number between accounts cheats all members of the Family or the shared email/number also get a VAC ban for that game, even if the other accounts haven't played it to prevent the use of alts to ban evade.

Phone numbers are a separate thing from Steam Families. Getting banned only bans the account playing the game and the account that owns the game. You won't get VAC banned if you play CS2 and your brother also plays CS2 and cheats, unless your brother is cheating in a way that also makes it detect the cheat on your copy of the game.

Found with a Google Search.
Info comes direct from Valve.

Yes, VAC bans can be shared between accounts, though the specifics depend on how the accounts are linked. If you are using a shared library on a computer with a VAC ban, both the owner of the library and the user who cheated can be banned. Furthermore, if accounts share the same phone number, a VAC ban on one can result in a ban on the other, even if that account doesn't own the game.


So uh, yes you can get VAC banned from a game even if you don't own/play it if you share a number or library with the user who cheated.
This is done to prevent users from using alts to evade the ban when the accounts are linked.