The re="nofollow" attribute

The rel=”nofollow” attribute is an easy way for a website to tell search engines that the website can’t or doesn’t want to vouch for a link. The best-known use for nofollow is blog comment spam, but the mechanism is completely general. Nofollow is recommended anywhere that links can’t be vouched for. If your logs analysis program shows referrers as hyperlinks, I’d recommend using nofollow on those links. If you have a wiki that anyone on the web can edit, I’d recommend nofollow on those links until you can find a way to trust those links. In general, if you have an application that allows others to add links, web spammers will eventually find your pages and start annoying you.