Tim Mullen, of www.hammerofgod.com, has produced the most comprehensive set of Computer Sets yet available. You can use these Computer Sets to import into your ISA 2006 Firewalls. Not only will these Computer Sets allow you to block connections by country, you can create your ISA Firewall rules so that you can accurately log where spam is coming from, and from where attacks are coming. There's no end to the usefulness of these Computer Sets!
Three cheers to Tim for providing these to the ISA Firewall community, free of charge.
Find these sets at: