Spamhaus reports that they have "uncovered a fake spam filter company which was pirating and selling DNSBL data stolen from major anti-spam systems including Spamhaus, CBL and SURBL, republishing the stolen data under the name 'nszones.com.'"
Ouch. I guess if you publish a free or easily accessed spam filtering tool, it is inevitable that at some point somebody would try to take the data and repackage it against copyright and against the data owner's wishes.
If you find yourself listed on this blacklist; don't fret. If what Spamhaus says is true (and I have little reason to doubt them), then this list is not really being used to block email. (And should not be used to block email.) Ignore it, stay listed, and eventually they'll move on to easier targets.
If you're a system administrator, DO NOT use any of the blacklists at nszones.com for spam filtering purposes. As its intent may not be above-board, I would have strong concerns about the possibility of listing things only to engender a payment for delisting -- for reasons having nothing to do with spam fighting.