IMHO Even the really large DNSBL's are barely used -- I think (much) less than 5% of total human mail recipients are behind a mailserver that uses one... --Phil -----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Big_Bandwidth Sent: Tuesday, July 23, 2002 2:14 AM To: nanog@nanog.org Subject: Security of DNSBL spam block systems What are the security implications of someone hacking a DNSBL (Real-time-spam-block-list) and changing the block list to include (deny email from) some very large portion or all IPv4 space? Given that a signifigant number of the spam blocking lists seem to operate on a shoestring budget in someone's basement, how can we be assured that they have sufficient resources to secure their systems adequatley, and monitor for intrusion 24x7? Unless I am missing something, this would seem to be a real handy and centralized method for someone to interfere substantially with the proper operation of a few thousand email servers and hold up global email traffic for a few hours. -BB