The Register of Known Spam Operations (ROKSO) is a list of over 500 professional spammers that is maintained by the Spamhaus Project, an organization dedicated to identifying and exposing spam operators. Any spammer known to have been terminated by three consecutive Internet service providers (ISPs) is added to the list. According to Spamhaus, the top 200 spammers on the list are responsible for 90% of all spam.
Typically, large-scale spammers move to another ISP as they become unwelcome on their current one. They sometimes disguise themselves as ISPs as a way to fool other ISPs into offering them connectivity to the Internet. Spamhaus also maintains the Spamhaus Block List (SBL); any IP address known to be associated with a spammer is included in this list. A special version of the Register of Known Spam Operations provides additional information for law enforcement agencies.