From Online Manual
An IP Address is a unique number that identifies a forum user's computer on the internet. Users can see their own IP Address under their posts and in their profile. The administrator can see every user's IP address. The IP address can be used to ban a troublesome user (member or guest). Because many users' ip address changes frequently (dynamic IP address), and because other users use proxy servers that cause multiple users to have the same IP address, it can be difficult to pinpoint one user with an IP-based ban.