If you have a site which allows for user comments, you should be aware that being lackadaisical on “monitoring” comments can have an SEO impact ( as recently revealed by Google). So why it’s important to have open discussion and feedback, there is a rogue element who feels it appropriate to add comments with useless links and unrelated topics. Simply put, being constructive is not their goal.  So what should you do if your site is full of spam and you want to avoid issues with your rank within Google’s search engine? Start a clean up as soon as possible by deleting spam comments and ban the spammers from your site. The next solution is to adopt security measures to stop any new spam activity. Here are just some ideas according to Google:

• Disallow anonymous posting.
• Use CAPTCHAs and other methods to prevent automated comment spamming. (We recommend ReCAPTCHA)
• Turn on comment moderation.
• Use the “nofollow” attribute for links in the comment field.
• Disallow hyperlinks in comments.
• Block comment pages using robots.txt or meta tags.

If you are using WordPress we highly recommend using Askimet and Bad Behaviour. Both of these plug-ins will reduce your spam. It also helps if you modify your discussions settings in the “Before a comment appears” section. We recommend checking both ” An administrator must always approve the comment” and “Comment author must have a previously approved comment”. Experiment what works for you, but we know default settings will not work.

If you are looking for more info, Google has recently written on comment spam and what to do when your meta tags are hijacked by spam.