Hello,
There are plenty of bots that crawl the web day after day searching for WordPress blogs to fill them with URLs in order to get publicity (SEO) for some sites… For example the case of my anonymous blog (this one) never got a real comment, but day after day it got around ~7 spammy comments…
Knowing a little bit about how to do and how the bots work, on the 99.99% of the cases they will go for the standard site/layout and will automatically fill the comment field and sent it. And successfully on low number of cases due blog missconfiguration, or so many real comments that could mix some real/spam comment those spam messages get live…
So there will be 2 ways to get rid of bots, setting up a filter like “Akismet” that will analyze all the comments and based on IP and word analysis will mark the comments as spam or not… (Anyway the comments will or could flood your spam folder and also ~10% will pass to you directly)
Or a most straight forward method will be change the normal site layout with a plug in or manually, for example to rename or add new fields, so the bots won’t know how to proceed. For this case I used the “WP-reCAPTCHA” plugin; it automatically add a captcha field to all the comments (and other forms if you want) and wont let nothing pass if the captcha is not correctly solved.
More Info:
http://wordpress.org/plugins/wp-recaptcha/
Regards,
AC