Huh? I think you do not understand. Do not mistake "cache hijack"
for "cache poison".
And to Randy's point about problems with open recursive nameservers...
abusers have been known to cache "hijack". Register a domain,
configure an authority with very large TTLs, seed it onto known open
recursive nameservers, update domain record to point to the open
recursive servers rather than their own. Wammo, "bullet proof" dns
as has been said here repeatedly, you should not be running servers,
recursive or not, on old broken and vulnerable software.