Back in the day when blogs were first starting, nasty spammers used to abuse blog commenting, and spam the comments with their junks links, trying to promote all kinds of junks porn gambling sites.

To combat this, Google implemented the “no follow” tag. This tag was picked up by wordpress and impelemented for URLs in comments as standard in their scripts. What it means is that URLs in the comments field are ignored by google, and pagerank and indexing are not improved for the target sites, from these links. The expectation was that this would disuade spammers from commenting on blogs.

“do follow” is one of most popular way to promote your website.

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