Spam is a big problem for any website which lets users contribute, and unfortunately blogs are no different. The more successful your website gets, the bigger your spam problem is likely to get too.
There are dozens of great WordPress plugins which help stop spam. In a few weeks I will showing you some of the best plugins which you can install to reduce spam however today I want to show you 10 simple things you can do to discourage and reduce comment spam.
1. Close comments after a set period of time
Comment spam is much more common in older articles as search engines can take a few weeks to fully index content (search engines are how many bots find articles to comment on).
WordPress allows you to automatically close comments after a set period of time. In your discussion settings area (e.g. http://www.yoursite.com/wp-admin/options-discussion.php) you can close comments after a set number of days.
If the majority of your comment spam appears in articles which are older, this is a step which would greatly reduce if not eliminate your comment spam. Find out the age of articles which are being spammed so that you can set the number of days accordingly.
Be aware that your site will get traffic from legitimate visitors too, therefore this step can be frustrating for those who want to leave comments. Whenever I have taken this step on my blogs in the past I have added a note to my comments area to encourage them to leave their comment in my discussion forums.
2. Only auto publish comments from those who have a previously approved comment
In your WordPress discussion settings page you can set it so that a comment will only appear if the commentator has a previously approved comment. This should greatly reduce comment spam as most spammers leave spammy comments from day one.
Be aware of the drawbacks of this option. Not only does will this rule take up a lot of your time, it can also hold back discussions on your site (particularly if you take several hours or days to approve comments).
3. Reduce the number of links in comments which require moderation
By default, WordPress will hold back any comments for moderation which have 2 or more links. This number can be changed. By reducing this number to 1 you will undoubtedly stop a lot of spam slipping through.
4. Blacklist common words, website URLs and emails
Some of the most common products being spammed on WordPress powered websites are pharmaceutical products and adult websites, though you may be getting spammed by other affiliate products or rival websites. By blocking keywords, websites and emails which are commonly spammed on your site you can stop a lot of spam from being published.
5. Blacklist the IP address of anyone who leaves spammy comments
Another thing you can do is block the IP address of spammers who are attacking your site. This is something which I always do when a spam comment is left as it only takes a few seconds but can stop a lot of spam comments in the future.
6. Make it clear that people must use their name and not their website name
People who leave spam comments usually enter their website name in the name field instead of their own name. This is a small pet peeve of mine as it usually indicates the person is only leaving a comment in order to get some traffic (it’s also less personal).
Discourage spammers by adding a note stating that commentators must comment using their name or alias rather than their website name.
7. Make it clear that irrelevant comments and short ‘thank you’ type comments will be marked as spam
Most spam comments are very easy to spot because they are either (a) irrelevant and have nothing to do with the article in question (e.g. generic comments that could be made in any article but usually make no sense) or (b) short and pointless (e.g. ‘great post’ ‘thanks’ etc).
So to discourage spam of this kind you can add a rules area above the comment field that informs visitors that you don’t tolerate spam and will remove comments which don’t add something to the discussion. It won’t stop all spammers but it may discourage those who were thinking of leaving a pointless comment.
8. Ensure your website comment links are no-follow
I have spoken many times over the last few years about why it is counter productive to make comment URL links do-follow. These links are no-follow for a reason.
Do yourself a favour and make sure your comment links remain no-follow. Not only will this ensure your sites internal PR juice is not greatly reduced, it will also stop people from coming to your site to leave cheap comments for a free link.
9. Remove your top commentators list
A top commentators list is a great way of thanking those who comment on your site on a regular basis (not only are these links displayed on every page, they are usually do-follow as well so pass PageRank juice to each site listed). I currently have one on the sidebar of WP Mods but I have had to remove it from other blogs I have owned in the past due to spammers.
Unfortunately, as your site grows and gets more traffic, you will attract people who only want to leave comments in order to make it into your top commentators list. If you moderate your comments every day then this might not be a problem as you can make sure that only those who leave good comments make it onto your list.
However, if you do not have the time to moderate comments every day or if your site is attracting a high number of spammers who are trying to break into your list, then it may be prudent to remove the top commentators list altogether.
10. Make people to register to leave comments
If you only allow registered users of your site leave comments you will greatly reduce spam. By their very nature spammers are lazy so it is unlikely that they will register on your site in order to leave a comment. It isn’t full proof but combined with some of the previous steps I have mentioned it could all but eliminate your spam problem.
You need to be aware that it can be a pain for visitors to register in order to leave a comment so the number of comments your articles receive will drop by a huge margin. I took this step a few years ago in one of my blogs and the level of comments dropped to around 10% of what it was before (in the end I removed the need to register because of this). This is something I would only advise you to do if you have a severe spam problem or if you really need more control over who can comment on your site.
Overview
I hope that this article will help those who are having problems with comment spam. Remember, there is no right or wrong way to configure your discussion settings; it really depends on your own situation i.e. how much time you have to moderate comments, how bad your spam problem is, how important comments are to the success of your website etc.
Unfortunately, the only step you can take which is 100% efficient in stopping spam is removing comments from your website altogether. It’s an extreme step but it’s one which a few people out there have taken (most famously Seth Godin).
It’s not something I would ever do with a blog though it’s something I commonly do with small content websites as the vast majority of comments I receive on them are spam. Note, it’s a good idea to create a forum if you close comments on a website with good traffic as people will naturally gravitate towards that to post their thoughts 
Make sure you subscribe to WP Mods as in a few weeks time I will be showing you some fantastic WordPress plugins which greatly reduce and discourage comment spam.
Please feel free to share your own anti-spam tips in the comment area!
Good luck,
Kevin
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