And among the users, which ones can I be sure about them being bots, apart from the ones that already posted spam? Those weird e-mail addresses are enough to tell?
The -12 timezone is a clear sign?
What I do, is that I delete all users that don't log in after they signed up. I usually wait a couple of days, and if they haven't logged in by then, I delete them.
To see if they have logged in after signing up, go to «Administration», «Users», and type a asterisk (*) in the field «Username» and hit enter. This will give you a list of all your users, and the ones marked in bold text have not signed in after signing up. Of course, this is only useful if you require email-verification.
Also the -12 timezone clearly indicate (for most forums) that it is a spambot.
What i really would like to see in future versions of PunBB, is that the users don't show up in the user list until they log in for the first time. That would really solve the problem with spambots, I think.