I just noticed that my dns server was being used as a caching dns server for some random host. In my log files, I was seeing ANY queries for x.h.ctrc.cc. When I looked at the cache, this was for some encoded data.
Using the documentation on this page, I was able to fix this problem. The way that I fixed this was to add the following to the options section:
// version statement for security to avoid
// hacking known weaknesses
version "get lost";
// optional - disables all transfers -
// slaves allowed in zone clauses
// optional - disable all recursive queries