From time to time, I get a rash of nonsense comments on my blog. The
text of the comment will look something like this: bmzps kjvl
ysaxhegqj zbmiye ybhpj cmyws qfuxg. Occasionally they contain links,
but if they do, the links are just nonsense, like the text. I use a
captcha scheme for comments, so presumably people are taking the time
to enter these by hand. I don't understand what the point is.  

I think the point is to see if you're using any kind of filtering.  

The funny thing is, I am using filtering which catches most of the
real spam, but it doesn't catch the nonsense because that doesn't fit
any well-defined parameters. So if they are doing this as a test, they
are wasting their time, since anything they really want to post is
unlikely to get through.

The plugin I mentioned turned out to be a total disaster

But who knows?

A follow up to this.  Seems this might be the intent of these messages:

http://www.anders.com/projects/sysadmin/formPostHijacking/

I don't see how the blog comments could be turned into
email exploits, but maybe I'm missing something.