I`m pretty sure there are zero day exploits working on 2.8.4, and the worm exploit have probably been zero day for a long time. Who knows, maybe years.

I voted its a trick question. If its safe enough ? Yes, its safe enough, if you dont run a critical site that is likely to get special attention from hackers, and store sensitive information in the backend.

http://www.number10.gov.uk/ is running WP and it should really attract some hacking attempts. Mike Little at http://zed1.com/blog may have modified it quite a bit though, and its probably on the safest of servers, but running WP safe is possible.