It is an unfortunate fact that for every good thing on the internet, there’s a hundred people trying to cover it in spam. Your blog is one of the good things, and no matter how small, someone’s trying to spam it.

As most of the spamming is being done by automated programs (bots) these days, it’s not personal & it doesn’t matter in the slightest what your blog is about; if the bots find a way to post comments, they will absolutely batter you with them, posting hundreds a day. I saw this with a simple PHP based guestbook I used on another site: first it was one comment a day, then a couple, then a dozen, and within 14 days a couple of hundred comments were going on, and I had to delete it.

There are a variety of ways you can prevent Comment Spam:

Switch off comments: The most drastic, but certainly the most effective. Do you really want comments on your blog posts? If not, switch them off. Speaking for myself though, I find it one of the best things about blogging, being able to interact with my readers, so I need something else. It is worth considering switching off comments, if you’re going to leave your blog for any great length of time though.

Moderation: Easily the best option, in conjunction with a plug-in, and until you reach the stage of 100 comments a day, it needn’t take very long. On my blogs, moderation is enabled on first time posters. Once I’ve approved the initial post, their details are saved, and all future comments go straight onto the blog. This method has worked well and the only comment spam I have seen (the rest was stopped by Bad Behavior before I saw it) I could mark as spam, and block the commenter from making any more comments. You could alternatively require ALL comments to be moderated, but if you build up a regular group of visitors, you will soon be drowning in comments to moderate.

CAPTCHA - (Word Verification) A letter or number entry of a sequence which has been obscured. Everyone is familiar with these simple tests, where you are required to type in a group of twisted, obscured characters, prior to entering a comment. Loathed by every comment leaver who uses them, I would be wary about placing them on my blog. Some sets are relatively easy to interpret, but others are so vague, it can take 3 or 4 attempts to get them right. Most blog readers won’t go much past the second attempt, and some have stated they won’t comment at all. As far as I am aware, this is the only standard spam protection available to Blogger users - I would suggest using only if comment spam has reached an unbearable level, and turning off again as soon as you are able.
CAPTCHA apparently stands for Completely Automated Public Turing test to tell Computers and Humans Apart.

Math CAPTCHA - This is appearing on more blogs, and I think is more preferable to the standard CAPTCHA. It asks reader to enter the result of a simple math question e.g. ’sum of 2+4′. Use, according to the intelligence of your readers….

PlugIns: WordPress users can benefit from the following plugins - they are all designed to stop comment spam before you see it: they have a risk of banning legitimate users, but used in conjunction with a good moderation policy, they can reduce spam comments to 0.

Bad Behavior - The plugin used on my blogs. Detects spambots by the way in which they make HTTP requests i.e. it identifies automated commenters & blocks them with a short error message. On my 2 blogs, Bad Behavior is stopping some 500 comments every 7 days, and no-one has yet mailed me to say that they were wrongly blocked. Of course, human spammers may enter comments, but: a.They can only do so many at once, and b.I catch them by moderating first time comments. To date, I have only had 2 of these comments, easily deleted.

Akismet - Now installed as standard with WordPress, Akismet works by referring all comments back to the Akismet server to be checked against a blacklist & other tests. If identified as spam, it is moved to a holding folder for moderation by yourself. If you use a free, or other host which blocks outgoing traffic from your webspace (Awardspace for one) you will not be able to use Akismet.

Spam Karma 2 - Another plugin with a good reputation, SK2 runs all comments against an updated blacklist and moves suspect comments into a holding area for your moderation.

There are dozens of other methods & programs for spam killing, these are simply the ones I am familiar with, and as with most things on Blog-Op are all free!