If you keep up a blog then you are probably well acquainted with comment spam. This is an inevitable fact of life if you allow comments on your blog (which you should in most cases). At Marketpath, we reached a point with our blogging platform where we were receiving a great deal of comment spam for our own blogs and many of our customers' blogs. Here's an example:
Image may be NSFW.
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Notice how well-written this comment is? Notice its perfect grammar and its amazingly descriptive word choices? That's sarcasm, of course.
The good news is that if you are using Marketpath CMS, you don't have to worry about this type of comment rearing its ugly head on your blog. Every comment must be reviewed and approved before others can see it and it's very easy to do so. You'll receive a notification about the comment and can quickly jump into CMS to approve it.
Most other CMS platforms provide some sort of comment moderation as well and may even run comments through an detection engine to determine how likely they are spam. The best tool for this, however, is using good ol' fashioned eyeballs. Not everyone who comments writes well so you'll want to be careful not to ignore legitimate comments.
Why do people spam your blog? The biggest reason is that they are trying to improve their own website's search engine position by creating backlinks to their site. They will embed keywords and utilize the URL field to create the link.
Marketpath helps eliminate spam not only by requiring approval of comments but also by using a REL="NOFOLLOW" tag in the links. This tag tells search engines to ignore the link and alerts most spammers (those with a decent understanding of SEO) to avoid it because they know they won't get any credit for the link. Marketpath also strips HTML tags from the actual comment. If a spammer tries to embed a link into the comment, it will be stripped and removed completely. And the final tactic we employ is requiring visitors to enter a number verification (captcha) so automated spamming systems won't get through.
All in all, comment spam is a fact of life and will continue to be for quite some time. Simple measures, like I discussed above, whether you're using Marketpath CMS or some other evil CMS platform, should be a standard part of the technology to keep these comments from ever seeing the light of day.
Here are a couple more posts about comment spam that may interest you:
Hard facts about comment spam (Google Webmaster Central Blog)
Spam in blogs (Wikipedia)