Serious problem with registrations

[Nikke]

I've recently discovered a very nasty problem with the registrations to my site. There is a LOT of new registrations with a drug name as username and with an email adress ending @hotbox.com. It must be some kind of automated process I believe. How can I make it end?

[Paul M]

Ban the e-mail domain '@hotbox.com' in the ACP banning options, also turn on image verification.