If you run a server you will notice allot of spam and intrusion attempts from specific blocks of IP’s. If you’re like me you get sick of server logs filling up with attacks from these networks.
The easiest way to stop them is to block them at the firewall. Here are the networks I block and I see about a 85% decrease in spam and intrusion attempts:
Amsterdam / Select Networks from Australia [list.amsterdam]
Korea / China [list.korea] [list.china]
If you’re using pf as your firewall and would like to add these networks simply use tables: http://www.openbsd.org/faq/pf/tables.html
If you plan on doing business with people from Amsterdam, Australia, Korea, China, or the Caribbean I would pass on adding these networks to your block list.