Spam in blogs also called simply blog spam, comment spam, or social spam) is a form of http://en.wikipedia.org/wiki/Spamdexing(Note that blogspam has another, more common meaning, namely the post of a blogger who creates no-value-added posts to submit them to other sites.) It is done by automatically posting random comments or promoting commercial services tohttp://en.wikipedia.org/wiki/Weblog http://en.wikipedia.org/wiki/Wiki http://en.wikipedia.org/wiki/Guestbook or other publicly accessible onlinehttp://en.wikipedia.org/wiki/Discussion_board Any web application that accepts and displayshttp://en.wikipedia.org/wiki/Hyperlinks submitted by visitors may be a target.
Adding links that point to the spammer’s web site artificially increases the site’s search engine ranking. An increased ranking often results in the spammer’s commercial site being listed ahead of other sites for certain searches, increasing the number of potential visitors and paying customers.
Read more: http://en.wikipedia.org/wiki/Spam_in_blogs