Tonight's update for Counter-Strike: Global Offensive includes just two items. The first is a fix for a UI issue, but the second is a nice improvement for their anti-cheat system, VAC.

Changelog for CS:GO for April 29, 2016
According to the updated VAC FAQ (linked above), this new system will ban all accounts associated with a phone number if one account receives a VAC ban.
VAC and Game bans apply to all accounts on a phone number
If an account that has a phone number registered to it receives a VAC or Game ban, all other accounts that used the same phone number at the time of the infraction will also receive a ban. If the other accounts do not own the game they will still receive the ban and be unable to purchase the title on that account. The phone number on an account that receives a ban will be suspended for three months and cannot be applied to another account during that time. The cooldown duration for applying a phone number after a ban will increase each time a cooldown is applied.

This feature is not enabled for all games and will be used at the discretion of the developer.

You may ask yourself, "who would be dumb enough to willfully cheat and associate multiple accounts to the same number?" Well first off, people are idiots. I mean, they're cheating in the first place so they already have that working against them. Secondly, if someone's son or daughter has an account tied to the same number a parent has their account tied to, it could result in some situations where a parent is none too pleased with what their kid has been up to.

Chances are though, most cheaters won't associate a number with the account and thus won't risk this sort of ban, but that still means that the Prime service should be a better experience for legitimate players.