Ban their IP ranges hostside via cpanel(Assuming you have it).
Ex, if their IP is 44.444.44.444 you'd enter 44.444.44.
Since the range is entirely that amsterdam bot's thing, it blocks a ton of bots.
Here's a mini-list of a bunch of bots' IP's.
http://pastebin.com/f4e6529c5
Also wise that you set to where you approve members first, then do a whois on the ip. If it's bad, block the range.