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The collaborative encyclopedia website will now automatically insert the rel="nofollow" attribute into link tags to tell search engines to disregard the links.

The attribute is an instruction for a search engine to ignore the link when it ranks sites in order to produce its results. The tag was introduced two years ago by the three largest search portals, Google, Yahoo! and MSN as a measure to deter spam on blogs. It is supported by a number of leading blog software producers.

Wikipedia's founder James Whales suggested the adoption of the tag because an increasing number of links were being added to articles simply to boost search engine rankings of the linked site. Links to a site are a key component of the algorithms that the engines use to estimate the value of a website: the more links a site receives, the greater its ranking; the greater its ranking, the higher it appears in search results.

Among the spamming that Wales had observed was the addition of links in the hope of boosting sites that were competing in a search engine optimisation contest.

Wikipedia itself notes that the introduction of nofollow has prompted much

Critics pointed out that this deprives many presumably useful websites of the benefits in search engine rankings from having a link on Wikipedia, wrote Michael Snow, a Wikipedia contributor, in the encyclopaedia's Signpost newsletter. 'Supporters argued that using the tag is part of good citizenship in the general effort to combat spam on the Internet.'

Philipp Lenssen, a blogger on Google and related issues, argues that Wikipedia is happy to accept links from other sites - boosting its own search engine ranking - but now gives nothing in return.

'The problem of Wikipedia link spam is real, but the solution to this spam problem may introduce an even bigger problem: Wikipedia has become a website that takes from the communities but doesn't give back, skewing web etiquette as well as tools that work on this etiquette (like search engines, which analyse the web's link structure),' he wrote.

But Matt Cutts, the head of Google's Webspam team, disagrees.

'I think it's the right call: the incentive to create spammy links on Wikipedia has been massively reduced,' he wrote. 'As one SEO person commented on a forum, "Yeah, that sucks. All those hours spent spamming wikipedia, gone to waste...".'

Cutts said that he does not expect the change to affect Google's rankings very much. He believes that over time Wikipedia will implement a method for contributors to approve external links and remove the nofollow attribute.