When creating websites using the WordPress platform, we remind ourselves and clients that WordPress is developed from a blogging platform, and while that creates wonderful opportunities as a content management system, it also allows those who have the knowledge to leverage the system to attempt to gain an advantage to their end only.
The first step you should do is activate your built in plugin, called Akismet. It will stop a lot of comment spam at the door. You will require to set up an account with them, to gain a code, but it is worth it.
Google used to measure the quantity of page links through comments as a factor in their page rank factor. When spammers find a website that has a quality Google indexing system, they will attempt to gain links from these sites, and bombard the open blogs with comment after comment which may seem legit, but a quick look at the URL of the website they list will show the true meaning for the comment. Even if a comment remains in moderation ( I.e. neither approved, deleted or marked as spam) it can possibly appear as a link to another site when Google index the site.
Comment spam is becoming a fast problem and needs management through the admin section of all WordPress websites in order to remove spam comments as soon as they appear. WordPress is set up to email when there is a comment that requires moderation. What needs to happen in these cases is a frequent management of the blog’s comments, and immediate deletion of comments that are designed to act as a link to a site that is not relevant to your site. The best defence against comment spam is just watching your comments. The faster you respond to comment spam on your site, the less likely the spammers will return. The best form of comment moderation is to mark all comments that are not genuine as Spam, rather than delete them. WordPress and Akismet will learn across the platform to watch out for the same comment structure of email and URL links, and deal with similar comments in the future.
A fantastic way to turn this situation around and use these submissions to your advantage may be to edit the comment. Have a look at the comment and see if it is linking to a site that is either selling a product or service. If so, you can delete the URL and received email address, and approve the comment anyway. This way, you get an extra comment on your blog, without the link the spammer looked for.