Can I log visitor frequency from the same account?

[MrSquid]

Is there a way to check the number of visits per-day, per-week, etc on a per-member basis so that I can look for a HUGE number of visits from a single member? (which presumably would have been happening on an ongoing basis)

I'm trying to sniff out users who may have given their ID and passwords to non-members. So I'd love to find a solution that's ID-based - not IP-based, because the people who aren't supposed to be on KNOW they shouldn't be there, so unfortunately they're not going to be dumb enough to post and have their IP logged.

Any suggestions?