Blue Frog is a company who operates a “Do Not Email” list, on the (optimistic) basis that spammers will vet their lists against it.
Reportedly, it’s been compromised. If this is true, I’m not surprised — as Dr. Aviel Rubin‘s report to the FTC of May 2004 regarding a Do-Not-Email list notes:
The scrubbing approach [to running a D-N-E list] requires that a list of live email addresses exist. While the party owning that list may be well intentioned, it is unlikely that such a valuable list would not leak out. History is replete with insider attacks, as well as external break-ins to highly sensitive sites, such as the Pentagon computers. The Do Not Email Registry represents the kind of prize that attracts hackers. In this case, the prize has monetary value as well. Once the list is exposed, there is no way to undo it.
Also, it’s almost inevitable:
If this service were running for some time, it is more likely than not that the plaintext addresses would leak at some point, given the history of computer security incidents.
Without hashing, a compromise of the registry database results in exposure of all of the registered email addresses. This is a total disaster. However, even exposure of a hashed list is a catastrophe. A spammer with a copy of a hashed list of email addresses is able to find out, for any email address, if the address is in the registry. The attacker simply hashes a candidate email address and sees if the hashed value is in the list. This is very powerful. [….]
Hashing provides absolutely no security against a marketer who obtains a scrubbed list and uses that to sell the addresses that were scrubbed by the registry. Whether or not the list is hashed has no impact on a malicious marketer in the scrubbing approach.