The mechanism of nofollow was introduced by Google’s Matt Cutts and Blogger’s Jason Shellen in 2005. Nofollow is actually a value that can be given to the “rel” attribute of an HTML link. The purpose of nofollow is to discourage comment spamming.
Many people thought that by commenting on blogs and forums and leaving their own website’s link in the comment was a great way to get the “back links”. Back links are the links of your website present on other websites. These referral links are extremely important because search engines, like Google, give a lot of importance to them. The more back links you have –the reputation of your website will increase in Googles eyes. This means that your website will feature higher on Google’s search results (which in turn means more traffic to your website).
In an attempt of getting more and more back links –people went on spamming other websites’ comment sections. Blogging platforms, like Blogger and WordPress, were severely hit by this trend.
Then Blogger changed coding of their platform and began to mark every link in comments as “nofollow”. This would mean that search engines should not consider these links as a back link. As a result spammers were discouraged as they were not getting any back links by putting links of their website in comments. This is how nofollow is used:
<a href="http://www.example.com/" rel="nofollow">Link text</a>
Nofollow has been successful but only in a limited way. Comment spam has been reduced by introduction of nofollow –but has not been completely eradicated. Although use of nofollow stops backlinking –but still the links left in comments can bring you traffic as visitors might click those links.