Search Engines Fighting Spam
Google, Yahoo and MSN, the three top search engines, have joined efforts to stop comment spam.
With the proliferation of blogs, forums and other public areas on the Internet, where people can post comments. Advantageously spammers have been flooding these sites with spam comments, trackbacks and referrers. They do this to increase the link popularity of their sites for certain keywords and therefore appear in a better position on search engine result pages (SERPs).
Fighting Comment Spam
Implementing a new attribute
rel="nofollow" on link postings you can fight comment spam.
<a href="http://www.example.com/" rel="nofollow">medical prescriptions</a>
Search engines will ignore links with the
rel="nofollow" attribute in the calculation of link popularity.
The solution is already available for some blog programs like Wordpress, who had released a plugin. This site uses Drupal and support was added through a filter, but it's only available in the development build, however it can be easily implemented to existing Drupal sites.