Just simply watching what they're up to is daft!, what good can it do you?, it'll waste your time keep checking hundreds and hundreds of logs, not to mention the amount of queries and server time to run such a thing, ban them and keep them banned
Have you set:
Admincp>User Registration Options>Allow Multiple Registrations Per User = No?
Admincp>User Registration Options>Require Unique Email Address = Yes?
Admincp>User Banning Options>Allow User to Keep Banned Email Addresses = No?
--------------- Added [DATE]1337547194[/DATE] at [TIME]1337547194[/TIME] ---------------
This is what you want if you want to see who's viewed what
https://vborg.vbsupport.ru/showthread.php?t=197487