Tracking login location / IP

[seo guy]

I know you can track the IP of a moderator in the statistics and logs, but I am wondering if there is a default option or a hack that would allow me to see if the same user logged in from multiple IP's or from multiple locations

Example: User logs in from Los Angeles at 10 AM - at 11 AM user logs in from Florida - (This would be physically impossible)

The reason for this question is I am trying to track down if specific users are sharing logins with others (A violation of our TOS) and allowing others to read / post / participate in private forums that should not have access -

Little help here?
Thanks