I'm getting users register just so they can put spam/phishing/virus URLs into their profile data, and are not posting. So can I ban them, or should I just delete them?
First you shall think why
would you like them getting banned? Do they disturb you or your forums existence? No, they only add the valuable count of registered members to your board. People coming to your board and seeing you already have 20 members registered is better than if they come and see there are only 2 members. The links they post in profiles, do not work for them at all. They are not indexed and not even highlighted for guests. You can also remove the URL field from the Profile completely, or modify parseUserInfo_user_website
function to let it output the different value for this field.