Two companies that were formerly on KnujOn's list, Beijing Innovative Networks and Joker, were issued warnings by ICANN and have since cleaned up their act, Bruen said in his report.

Being on KnujOn's list is "definitely embarrassing" for any company, but it shows that companies like Network Solutions could do a better job at kicking the spammers off their networks, said Richard Cox, chief information officer with Spamhaus, another antispam group. "They've got a very large volume [of domains]," he said of Network Solutions, adding that "they're not the easiest people to deal with."

According to KnujOn's report, Network Solutions domains were linked to around 580,000 spam messages, and Wild West's to just over 50,000.

Network Solutions takes spam seriously, said spokeswoman Susan Wade. "We continually review and improve our systems; however, no matter how good our systems are, we are still reliant on the speed at which stolen information is reported," she said via e-mail. "Unfortunately, there will continue to be a window of time at which spammers will operate. Our goal is to significantly shorten that period of time."

KnujOn's top ten spam-related registrars is as follows. The ranking is based on a variety of factors including the amount of spam associated with a registrar's domains and the percentage of the registrar's domains linked to spam.