Fair enough @jab1
I would assume there is some kind of bot making automated signups, so it could maybe a case of modifying the code slightly (the signup process) to beat it (for now).
Unless they are paying someone the equivalent of 2p per hour to do it manually - then it becomes more difficult I suppose.
I know what a pain in the backside all of this is, so I understand the pain this is causing Lithium, the Mods and the Admins on here.
One way I guess is (I know from my phpBB2 days) is restict new signups so they have to be manually approved first. Though that is a pain in the backside as I would assume it would create a lot more work for people on here.