If you want to get serious with Blogging and use WordPress you need to use the self hosted WordPress software preferably on a shared or a dedicated hosting if possible. With popularity you will get more traffic on your site and that will also increase the number of comment spam.
Comment spam can really get annoying and may also damage the reputation of your website that took months or years to create. Furthermore the comments posted on any WordPress post also get indexed by the search engine. So comment quality does matter.
Here are some steps you can use to reduce WordPress comment spam
I would suggest you enable comment moderation for everyone including registered users. WordPress does give you an option to send new messages into moderating queue that satisfy certain conditions like from guest users or comments that have links, before it is made live.
This is a good option to check and approve only quality comments. Though this can become very tedious especially if there are too many comments. But then it’s better to check and approve rather than to go through all comments to find and remove the spammy ones.
You should also monitor registers users if you want to maintain good quality comments. Remember the comments get indexed and hence are as important as your content.
Activate close WordPress comment after 60 days
WordPress does come with an option to close comments automatically after specific number of days as defined by you. Just login to WordPress admin and go to discussion on settings menu. In other comment settings you will find the check box with text automatically close comments on articles older than _ days. Choose 30 days or more or as per the traffic on your site.
Why should you close WordPress comment after specific days?
Well comments are important they add more value (content) to your existing post. But many use it for their own advantage to get links back to their site or for spamming and reducing the quality of the page by posting duplicate content or poor quality content.
A new post will get many comments because of its freshness, statistically most quality comments are received when the post is new. When a WordPress post gets older you will find that many comments really make no sense hence it does make sense to disable comments on such post. With WordPress you can automatically do that after specific number of days.
There are many Captcha / re-Captcha WordPress plugins available that will add a verification process in your comment form that users need to confirm. This is the best way to keep out automated spam bots and to make sure the output is generated by a real person. However this will not stop certain people are real and are paid to spam on high traffic sites. But then you are making them do all the hard work that results in nothing.
Switch to third party comment system (Disqus or IntenseDebate)
Use this only if you are unable to manage too many comments and really have no time to go through each and every comments. However when you use the third party comment system the comments are not indexed by the search engine as they never add up with content. I would really want to avoid this.
Things that do not really work
Blacklisting common words or IP address is just a waste of time as spammers will not rely on one IP address and by misspelling they can get through the word filter.
Using these simple methods you can reduce comment spam drastically.