Link building was an easy way to adjust the search engine
algorithms and many junk emailers tried to take advantage of this by building
link systems which gradually lead to the creation of what is generally known as
black hat SEO.
Google has become very intelligent in recognizing black hat
techniques and with the introduction of Panda and Penguin they have managed to
solve the problem and protect their search serps from spammers. Of course there
are still exclusions but they are doing advancements in every new release of
their ranking algorithm and very soon non-e of these tricks will work.
To “follow” or “nofollow”
In addition to the over and in order to give webmasters a
way to link to a website without passing any ‘link juice’ (for example in the
case of ads), search engines introduced what is known as the “nofollow” link. This
is a special tag you can add to a link (for example: “ <a href=http://www.somesite.com
rel=”nofollow”> Some Site </a> ) that tells search engines not to
count number the particular link as a ‘vote’ to the referenced website.
This was done so that you can link other websites from yours
without having taking the risk of being caught for selling or swapping links.
As a rule of thumb, you should add the nofollow tag on all
your external links (within your pages) that go to websites you cannot trust 100%,
to ALL your opinion links, to ALL your blogroll links and to ALL banner ad ad
links.
To know more click this link