How many North Koreans "sleeper agents" do we actually have inside the USA, that companies see this as a legitimate threat? Shutting down an event because some

How many North Koreans "sleeper agents" do we actually have inside the USA, that companies see this as a legitimate threat? Shutting down an event because someone is able to say "remember Sept 11" says more about our own government than it does theirs. We should not be at the point where anybody can cause a disturbance for something they don't like just by uttering threats.