Spam bot nets are an epidemic, they scrape content, work log in and post comment spam automated scripts, they use hijacked PC's and their respective IP addresses, these computers become part of their zombie network and have been taken over by spyware scripts unknown to the average computer user.
All should encourage everyone they know to run Spyware software like Adaware and Spybot Search and Destroy to remove the spyware from their computers that bot net operations use to harvest zombie PC's for their bot nets.
Webmasters can work with
Distributed Spam Harvester Tracking Network | Project Honey Pot together to stop them before they hit your server.