The original purpose of NoFollow was to stop comment spam on blogs. What is comment spam? Comments posted for the sole purpose of establishing an outbound link in order to inflate PageRank or promote commercial services, automated by web bots. They are easily recognizable because they frequently contain non sequiturs, self-contradictions, and/or comments entirely unrelated to the original subject, not to mention innumerable spelling and grammatical errors. And they always contain a link. A typical post might be “I disagree with some points, but think your article is really great.” Any web application which accepts and displays links submitted by visitors is a potential target.
The proliferation of comment spam had become a systemic problem on blogs, wikis, guestbooks, and other publicly accessible discussion boards. In some places, it was difficult to hold a coherent conversation because so much spam was being posted. And while there had been many attempts to combat the problem (such as CAPTCHA validation, blocking specific keywords, disallowing consecutive submissions, or disallowing links entirely), none of the solutions available at the time were making a significant difference. So in early 2005 Google’s Matt Cutts and Blogger.com’s Jason Shellen designed the NoFollow attribute to address the situation.
Example of a NoFollow link in HTML code:
<a href=”http://www.example.com/” rel=”nofollow”>discount drugs</a>NoFollow tells search engines “do not use this link to influence PageRank,” which practically revolutionized blog comment areas overnight. Four years later, it is still possible to find comment spam, but it’s less than one percent the problem it used to be.
What NoFollow does not do: it cannot block access to content, or prevent content from being indexed by search engines. (This functionality can be provided by other means, such as the Robots Exclusion Standard.)
Additionally, individual search engines interpret the use of NoFollow in different ways. Google (who participated in the design of NoFollow to begin with) will not use the link for ranking or index the “linked to” page, and will not display the link or pass anchor text to search results unless the page has already been indexed. Bing behaves almost identically, but will always display the links. Yahoo! will not use the link for ranking purposes, but will always index linked pages, display links, and pass anchor text to search results. Ask.com ignores the NoFollow attribute entirely.
So what are DoFollow links, then? It’s an internet slang term, which simply means a link is not using the NoFollow attribute, and can therefore be used to provide PageRank power.