34,000+ VAC bans and counting just today. Valve cleaning up for next TF2 update?

Also Valve doesn’t have any obligations in this regard, because you agreed so in the Subscriber Agreement:

C. Your Account

When you complete Steam’s registration process, you create a Steam account ("Account"). Your Account may also include billing information you provide to Valve for the purchase of Subscriptions, Content and Services and any physical merchandise offered for purchase through Steam (“Hardware”). You may not reveal, share or otherwise allow others to use your password or Account except as otherwise specifically authorized by Valve. You are responsible for the confidentiality of your login and password and for the security of your computer system. Valve is not responsible for the use of your password and Account or for all of the communication and activity on Steam that results from use of your login name and password by you, by any person to whom you may have intentionally or by negligence disclosed your login and/or password in violation of this confidentiality provision. Unless it results from Valve’s negligence or fault, Valve is not responsible for the use of your Account by a person who fraudulently used your login and password without your permission.

That said, don’t do Family Library Sharing with your little sibling if they might be cheating, either.

Will I be punished for any cheating or fraud conducted by other users while playing my games?

Your Family Library Sharing privileges may be revoked and your account may also be VAC banned if your library is used by others to conduct cheating or fraud. Additionally, VAC-banned games cannot be shared. We recommend you only authorize familiar computers you know to be secure. And as always, never give your password to anyone.

/r/tf2 Thread Parent Link - steamdb.info