Rel=nofollow inside hyper link tag to prevent PR flowGoogle has started suggesting webmasters to use the tag rel=nofollow in all the hyperlinks which users create in blogs, comment posts and other similar areas. This is used to prevent spammers from getting undue credit at different sites by posting URL pointing back to their own sites. Google algorithm gives weight ( for ranking ) to back links to a site so spammers tries to post their site urls at different places in internet particularly in comments or in sites where user generated contents can be displayed. Google suggest that all the scripts which allows such back links should add a tag rel=nofollow within the hyper link tag. This way google algorithm will discount the credit the spammer sites get by posting such links.
Here is an example on how it is used inside hyper link tag. The second line shows how it is to be used inside PHP script while using echo command.
<a href=https://www.example.com rel="nofollow">Visit this site</a>
As per google if site A has a link to site B then it is considered as a vote of site A in favor of site B so more links points to site B more its reputation reflected in terms of ranking goes up. So spammers always looks for ways to gain back links to their sites by posing URLs every place possible. To prevent this script can automatically add the extra attribute rel=nofollow to the links to tell google robots and its algorithm to discount the vote or PR ( page rank ) benefit it gets from this link
No negative vote or impact
But this does not mean by adding the extra component rel=nofollow we are telling google to penalize or degrade the targeted site. If this is not taken care then any one can intentionally bring down other sites by posting its URL at different blogs and forums.
Should we use this for internal linking
This is a big question. The original purpose of this tag was to prevent comment spam but webmasters found it is useful in many other instances. It is clear that link juice ( or Say PR ) flows through links so we need not pass this to each and every page we link. For example some sites use this for linking to contact us page or disclaimer page. These pages are not supposed to bring any direct traffic to the site, nor they are there for better ranking so webmasters need not be given ( or pass ) extra PR benefit while linking from other pages.
Linking for external sites
Some time we point links to other websites as an example to show how a script works or for a demo. By using this tag for external websites we need not pass the PR benefit to external site. We can use this tag for external linking where we display ads or display text links as an advertisement or as a paid link. It clearly tell search engines about the purpose of displaying such ads and site can avoid penalty related to link buying and selling.
By adding rel=nofollow inside our hyperlinks we can prevent flow of credit or Page rank to pointed site but that will not prevent robots to crawl the target or index the page.
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