steam
Today some jerk joined the Arqade group on Steam and started spamming people with links to a lookalike phishing site. You know, like this but with "store.steampowered.com" instead of "twitter.com":
Image from the OpenDNS Phishing quiz. Hint: this one is a phish.
Now, I've kicked him from the group and flagged his account, but… it's a public group! Anybody can join. We'd rather not change that and still keep him out.
Is kicking sufficient? What else can I do?
You can use a feature called "Family View" to restrict what your kids can do with your Steam account, including preventing them from accessing the store. This works by setting a 4-digit PIN that is used to log in as an adult "within" your account.
You can enable this and configure what parts of your Steam account are off-limits by going to Settings → Family and clicking on Manage Family View.
You'll want to leave the Steam store checkbox unchecked.
When I open steam and go to my group, I click "edit group permissions" under Admin tools At the top it says:
Public - Anyone can join
Invite Only - People can only join by being invited
There you can select a circle.
This should do it. Not that hard?
In your case when you click: "visit admin page" go to edit group permissions on the right.
Best Answer
You can't ban people from groups permanently, unfortunately.
What you can do is to report people via their profile and Steam will have a look at it.
You can also ban him from the groupchat.