As an extension of its previous efforts to discourage spam, Wikipedia now has the nofollow tag implemented throughout the site. This came after Jimbo Wales reversed his previous position that the feature should be disabled on Wikipedia itself.

The nofollow tag (the attribute rel="nofollow" added to a hyperlink) serves as an instruction for the search engine's spider as it browses the links on a webpage. Its effect is that the link is not considered when the search engine algorithm ranks sites in order to produce its results. The tag was announced two years ago by the three largest search portals, Google, Yahoo!, and MSN. Originally implemented as a measure to deter spam on blogs, it was also supported by a number of leading blog software producers.

In the MediaWiki software, the tag was added soon after the initial announcement and is part of the default code applied to external links. Since its introduction, it has been enabled for nearly all Wikipedia languages, but for a long time remained disabled for encyclopedia articles on the English Wikipedia. At the outset, there was a lot of discussion about how and where to apply the tag, including two polls on the subject. The developers made clear that it would remain at least on "unattended" wikis that were vulnerable to spam, but Wales expressed the opinion that it should be turned off for the English Wikipedia.

As a result of this discussion, the use of the nofollow tag was suspended on the English Wikipedia. After a patch was added to MediaWiki in 2006, allowing the tag to be enabled selectively by namespace, nofollow was then applied to the English Wikipedia except for actual articles in the encyclopedia.

In confirming the latest change to full use of nofollow, Chief Technical Officer Brion Vibber explained that Wales had requested the switch. He also mentioned reports of edits that were adding external links in hopes of boosting sites competing in a search engine optimization contest.

A similar contest held in 2004 already spilled over into Wikipedia. Offering a prize for the top position in a Google search on the made-up phrase "nigritude ultramarine", it prompted the creation of a Wikipedia article for the term. When an edit war about the contest ensued, the article was ultimately protected for the duration of the competition.

The change has prompted considerable debate, much of which revisits points raised when nofollow was first implemented. Critics pointed out that this deprives many presumably useful sites of the benefits in search engine rankings from having a link on Wikipedia. Supporters argued that using the tag is part of good citizenship in the general effort to combat spam on the internet.

In a different take on the issue, Philipp Lenssen expressed disappointment with the move, arguing that it was actually poor etiquette for Wikipedia because outside links are part of why Wikipedia ranks so well in search engines, so that it now "takes from the communities but doesn’t give back". Lenssen argued in favor of more sophisticated applications of the tag, such as time-sensitive removal for links that remain long enough to have been reviewed for usefulness. Google's Matt Cutts expressed confidence that Wikipedia could develop better methods of handling the issue in the future, but said that in his view this action was "the right call".