Does s2Member track visitor IPs?
Yes. s2Member's Unique IP Restrictions will help you prevent a security breach.
Tracking Users by Their IP Address (Location)
As with any membership system, it is possible for one member to signup, and then share their username with someone else; or even post it online for the whole world to see. This is known as link sharing (aka: username sharing). It is not likely that you'll be attacked in this way, but it's still a good idea to protect your system; just in case somebody tries this.
s2Member's Unique IP Restrictions work for Membership Level Access (account logins), Specific Post/Page Access, Registration Links, and other secure entry points. In all cases, the rules are simple. A single username, access link, and/or entry point; is only valid for a certain number of unique IP addresses. Once that limit is reached, s2Member assumes there has been a security breach. At that time, s2Member will place a temporary ban (preventing access) to a specific post/page, or to an account associated with a particular username. This temporary ban, will only affect the offending link and/or username associated with the security breach. You can fine-tune this behavior through configurable options.