Multiple Logins per user/ip address in logs

[zeroth]

It would be nice as a security feature to disable multiple logins per user. I have found a few people that have given out their credentials to random friends without asking me and whom I don't know personally. Is there a limit on multiple logins per user at all?

Maybe sticking a Session ID into the Database and performing a check when a user logs in. Then throw out a warning that more than one person is attempting to use the same login? Can this be done without waiting for an update?

Also, logs with ip address would be helpfull as well.

I found some information by searching the forum but I've not found anything in feature request.