Updated Norton DNS to the new IP's:
199.85.126.30
199.85.127.30
Tested connecting to an Adult site and it went through OK, not blocked.
Changed back to the old IP's:
198.153.192.60
198.153.194.60
And it was blocked.
Also tried with various other sites too and they were all allowed through.
Have flushed DNS cache, cleared browser cache's etc and no difference