If you aren't going to install an anti-spammer mod then I highly suggest changing your activation settings "User registration settings->Account activation" to either "By User" or "By Admin". I suggest the "By User" as it would be hard for admins to determine if the user is legit right now in most cases.
The benefit being that 99% of the accounts are not human users but some form of bot and they won't activate the account or at least I have not had any of the 60 plus bogus accounts thus far do it. Likewise in both cases it will prevent your current members from seeing the bogus accounts (including nasty profile links), the bogus accounts can't create posts (if your forum posting settings are set with some basic logic) and thus your members are protected from possibly clicking a link that leads them to a virus.
Plus it is very easy to delete accounts from the user activation screen in ACP verses finding them manually and deleting them.
Sad this crap has to happen but I am sure the phpbb team will find something to help soon.













