One of the major problems that faces search engines is spammers trying to manipulate their ranks using black-hat search engine optimisation (SEO) techniques. One of the ways they do this is by posting their links on blogs and in forums, hoping that search engine spiders will pick up the links.
This practice was causing such a problem that Google introduced a new attrbute for hyperlinks; nofollow. The nofollow tag can be added by webmasters to their pages to show that they do not endorse the outbound link. When a search engine spider reads the hyperlink, if it detects the nofollow attribute it will ignore the link.
It is important to note however, that all search engines treat nofollow differently. The 3 big players, Google, Yahoo! and MSN all discount links with the nofollow attribute, but in different ways. Most importantly however, is that nofollow links are not counted as part of Google PageRank.
Despite this, spammers continue to post keyword-flooded hyperlinks into blogs and forum posts. Why do they do this?
The answer is simple, they don’t get penalised.
Google have come out and said on many occasions that they don’t penalise sites for anything that your competitors could do to harm your rankings.
Let’s imagine for a second that Google and the other search engines penalised sites for putting their links all over blogs and forums. This would certainly stop spammers placing their links all over the place, but would open up a new market; link sabotage.
This would mean that your competitor’s could go around putting your link all over blogs and forums and as a result, you would be punished.
For this reason, Google don’t punish you for putting links everywhere, but through the use of the nofollow attribute have found a way to simply not count the link.
This is currently the fairest system, but is not providing any disincentive to spammers spreading their links. Having said that, it’s still the best way to solve the spamming problem.