This article is tagged because it NEEDS REVIEW. You can help the Joomla! Documentation Wiki by contributing to it.
More pages that need help similar to this one are here. NOTE-If you feel the need is satistified, please remove this notice.
The best method of dealing with a problem user is not to delete the account. It is better to simply block them from logging in. This is true for a few different reasons.
First, it is temporary, so it can be used to suspend rather than ban. Second, if you are requiring your users to authenticate via email and you are not allowing duplicate email addresses, it will make it slightly more difficult for them to simply recreate their account or create a new account.
While there are some extensions that will allow for blocking by IP address, Joomla! does not include this functionality by default. Additionally, please note that as discussed in the Security and Performance FAQs,this method is not recommended because it is ineffective. First, because the problem user may not actually be the owner of the IP address. Second, because most IP addresses are non-static, so they will change periodically. For example, if the person is using a wireless laptop, and simply moves to a different wireless router, they will end up with a new IP address.
Depending upon your location and the nature of the activities of the problem user, there may be certain legal actions which are entitled, or even required to take. If you feel this may be the case, please consult an attorney or the appropriate authorities in your area.