I haven't seen this happen since I have been our team leader. Our team is listed as "closed" and "by invitation only." However, yesterday, a new player suddenly showed up as a new member. After checking with everyone on our team, I have confirmed that no one sent an invitation to this person. Also, as team leader, I didn't invite or okay any request to join. Is this a bug? Very curious as to how someone could do this. Any ideas would be appreciated. I have left this new person on our team for the time being but don't want to post the name here.

"Invite only" is not an absolute - any player knowing the internal team ID number can join. Since that number is in various places (including on one of the team info pages), it's not a secure system to prevent members from joining.

You are however justified in removing the member from the team if you want to - just send them a message to explain that the team is invite only and that they should contact you about membership before joining.

Thanks Wesley. I changed our setting to "Closed." Didn't realize that the invite only had a loophole :-).