How do I tell if another user is using the account of another?

[Glowbot]

Some people are trying to snoop on my forum, and I think they are using a members account.

How can I tell if they are?

Can I only see the IP they use when they are online?

[Kermit]

The IPs of users are actually logged in their profiles,so you can see there which IPs they have already used

For checking IP locations you can use this site

http://www.maxmind.com/app/locate_ip

[Glowbot]

Oh thanks that's interesting... it only shows if they post though? am I right?

[Kermit]

Oh thanks that's interesting... it only shows if they post though? am I right?

If they login with new ip,the ip will be shown also on their profiles,even they will not make any post with that new one

[Glowbot]

which section exactly is the list of all the IP's used?

Summary
Show Stats
Show Posts
Track User
Track IP
Show Permissions

[Kermit]

Track User should do that thing