This article here describes how Facebook uses a PHP script to handle links to other websites to devalue the pagerank value.

Are all large website owners (particularly ones like Facebook who allow users to post whatever they like including links to websites) responsible for implementing such preventative measures or do search engine owners also have ways of preventing this type of exploit? Since posting a link to your website on all major websites could potentially be exploitable into making your website appear larger than it really is.

Also, how does passing the link through a PHP script devalue the backlink? Does it prevent search engine bots being able to navigate the links properly?

  • No need for a redirect script. It is much easier to use nofollow May 21 '19 at 18:25
  • @StephenOstermiller Thanks for the information, I wasn't aware this was the best practice.
    – Dominic
    May 23 '19 at 15:27

It's in the interests of every site owner to prevent "backlink exploits". Any user-submitted content (unless perhaps if it is heavily moderated or submitted by trusted/senior members) is "untrusted". If content is untrusted then any outbound links (if allowed at all) need to be nofollow. This should be standard practise for any site.

The "redirect script" can prevent the link passing "PageRank" since the script can potentially filter out bot traffic. The script can also be blocked by robots.txt, so any "good" bots won't crawl it anyway. This script can potentially prevent the bot from even seeing the destination of the link.

But as @Stephen pointed out in comments, you don't need to use a script to prevent the mainstream search engine bots using the link to pass "PageRank". A rel="nofollow" attribute on the anchor is sufficient to prevent PageRank being passed. However, bots can still "see" the link and potentially crawl it (although Google reportedly does not).

A "redirect script" can also allow the site to more easily track the link and gather user stats on those that click it.

However, Google (and probably other search engines) reportedly don't allow links on social media networks to directly affect ranking anyway. So, social media links don't pass "PageRank" by default. Having said that, Google would seem to be able to measure social engagement to some degree and this may play an indirect role in ranking.

  • Thanks for your thorough answer DocRoot. Here I was thinking I had to go some convoluted route when in fact nofollow is the simplest way. Interesting to know that Google specially filters social media links too.
    – Dominic
    May 23 '19 at 15:26

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