Hi Markus
So, what alternatives are there?
How about using services from Dshield (http://www.dshield.org/howto.html) or Threatstop (http://www.threatstop.com/IP-Reputation-Service-Overview especially step 5)
Basically you submit your logs and they do the lookup for you and you can benefit from getting offendig IPs from other ISPs.
Regards
Jean-Pierre