Blocking Wordpress comment spammers by User-Agent

I have been plagued with automated comment spam lately, it is still at a level where its managable manually but..... I am lazy.

The comment message itself is nearly always along the lines of:

It would appear to be more of a test message, blogs that accept the comment will probably be hammered with real spam at a later date.

I use ModSecurity on my server and wondered if there was an easy way to filter out these requests before they even reach Wordpress. I dug out my access_logs looking for the offending requests. The programs being used to post the comment spam appear to be quiet simplistic, posting directly to "wp-comments-post.php"

Others are a little more sophisitcated and at least bother to change the default User-Agent:

I crafted a very simple ModSecurity filter to catch these, although it is a little crude, it will only trigger when the listed User-Agents send a request to "/wp-comments-post.php". Adjust as required:

Related Links
ModSecurity - http://www.modsecurity.org/