I was sharing my library not knowig about it, with random person I don't know

[skittlez]

Hi, I just discovered that family Sharing is a thing and wanted to use it for the first time. I got on this site
https://store.steampowered.com/account/managedevices

And I saw random russian guy is authorized and I was sharing my games with nim the whole time, dunno how he got this, I swear I have never accepted anyone. I just clicked "revoke" and hes gone, How he got access to my games? Should I worry about my account now?

[Cathulhu]

Yes, you should. Someone at some point logged into YOUR account on THEIR machine to authorize the sharing.
So, if you didn't authorize it, your account is compromised.

[jasoncollege24]

Your best bet is to change your password to one that is more secure, and ensure that no other unauthorized devices have access to your account. you should also consider enabling SteamGuard, so that two-factor authentication is required to sign in.