Unwelcome comments

Running 2.0.2. A few weeks ago some comments started appearing that were out of left field (user did not register/sign in, etc.). All of them are spam/ads, and I mark them as such. Next day there are more, sometimes 5-10 at a time. Interesting that they always hit the same post in the blog.

Obviously somebody has a script that is getting around things. Any way to combat it?

Thanks.

John