Can someone other than people I invited join my group?

Question

What happens if a person I did not invite joined my group but is only phis-hing for personal info from other members who have already joined before him?

Answer 1

To go along with the first comment, make sure to set your group settings so that new members have to be approved.  Don't make the group "public" which allows anyone to post without being approved.  

Answer 2

You're talking about Yahoo! groups, right?  You can ban the person from your group.  Go to the Members link in your group, click on Edit Membership for the member you want to ban, and then click on the Ban Member button in the lower right corner.

You can also set up your group so that you have to approve any one who joins.  Go to your group's home page, click on Management.  Then click on Membership under Group Settings and then on (edit) nest to Membership Type and Welcome Message and change your group to Restricted.