Underwood also said that it was unlikely that a spammer would have been able to get an individual at a major ISP to install a "no route" to Blue Security, as Reshef claimed. "These are not the kind of networks where people can sneak in and make routing configuration changes" without logging that change or discussing it with others, he said. "The suggestion that some Russian spammer could bribe someone to install a no-route" is hard to believe, he said.

John Levine, chairman of the Internet Anti-Spam Research Group, said that other antispam efforts have been similarly targeted as well. But they did not involve an ISP. And neither did those who were attacked respond like Blue Security did, he said. "If you know you are under a DoS attack, pointing your DNS at other parties is irresponsible," he said.