Instead, one spammer compared the scrubbed and actual e-mail list to derive the addresses of Do Not Intrude members, and then began targeting them, Reshef said.

An attack also took Blue Security's Web page offline in the past two days, which Reshef believes is related to the spam campaign against Do Not Intrude members, although the company is still researching the problem.

Blue Security hopes to have its Web site back up soon and Reshef said it is undeterred by the attack on its members.

"This is a sign that (Do Not Intrude) is working. We've finally created something that spammers actually care about," Reshef said.