Links with irrelevant hypertext hurt SEO 

SEO Superstitions: Irrelevant Anchor Text

The claim is that if a page or site gets a lot of incoming links with irrelevant keywords in the anchor text (the hyperlink text that people see as the link), it will lose its position for the keyword. For example, suppose you are the Widget company. You have 50,000 incoming links that all say "widget" and Google returns your site as #1 when people search for widget. Your competitor could supposedly make 100,000 links that all say "Bad Junk" and cause you to be listed as #1 for bad junk and to lose popularity for keyword widgets. Curiously, it seems nobody knows if this is true. One defect in an algorithm like that, is that might "detune" pages that get linked from blogs in this way "Joe Johnson wrote here that..." or articles linked with the word "more" or "continued," not to mention all the home pages linked with the word "home." It could be true. It should be a rather simple experiment to try, but either nobody tried it, or they are not telling. I am trying this out and will write up the results. It will probably take a few weeks before we can say with confidence that you cannot move a top placed Web page with irrelevant links, but that seems to be the case as of now.

Update - Based on the evidence of my little experiment, it seems unlikely that you could downgrade a page's position for a keyword simply by linking to it using a different keyword in the Anchor Text. I targeted a page of my own that is top ranked in searches for the keyword Sexonomy in Google. Getting that rank was easy of course, because nobody cares about Sexonomy (it is not quite a made-up word) and there are only about 370 pages that deal with it. I created thousands of links to that page with anchor text "Mysterology." The page is still top ranked for Sexonomy. An interesting observation is that the page is now top ranked for both search words, though the word "Mysterology" doesn't appear in the target page at all.

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