The Nofollow Attribute

In early 2005, Google announced that hyperlinks with rel="nofollow" attribute, would not influence the link target's ranking in the search engine's index. Yahoo and MSN search engines also respect this tag.

The purpose of the rel="nofollow" attribute is to create HTML links which can be viewed and clicked by normal web users, but which will not be counted as a link by the search engines.
From now on, when Google sees the attribute rel="nofollow" on hyperlinks, those links won't get any credit when Google rank websites in their search results.

For example, this is how the HTML markup for an ordinary link might look:

<a href="http://ibytes.blogspot.com">ibytes</a>

This is how the link would look after the nofollow attribute has been added,
with the attribute portion shown in bold

<a href="http://ibytes.blogspot.com" rel="nofollow">ibytes</a>

This would also be acceptable, as order of elements within the anchor tag
makes no difference:

<a rel="nofollow" href="http://ibytes.blogspot.com" >ibytes</a>