The bottom line is - "If you link to sites that are banned by Google for spamming, you are inviting the risk of getting banned for linking to a bad neighbor."

Every business needs a product to sell and the quality of the product is very important for the success and failure of the business. The product of a search engine is relevant information.

Each of them has got an unique algorithm that ensures that the "best" quality and "most relevant" information will be displayed first. Anyone trying to manipulate the search results is actually trying to affect the product quality of the search engines. And the search engines can not simply afford to let anyone manipulate their results nor can they let anyone misuse the advantage of having a high rank.

Google depends on an algorithm called page rank while ranking web sites. Pagerank is a numeric value calculated after analyzing the inbound links to a site. A site with a PR value 7 is considered to be more important than a site with PR value 6.When a site with a high PR value links to another site, a certain amount of the importance is transmitted to the linked site. Pagerank is a vast concept and is however not the subject of this article.

Pagerank uses a very sophisticated technology and is very difficult to manipulate. However, spammers always try to find loopholes so that non-competitive sites can get into the top positions. So the people behind Google are constantly updating and improving their technology to be able to keep up with the standards of their search results.

Due to these modifications new quality sites get in the top ranks, the sites that do not maintain the ethics of search engine optimization even get banned from the search engine index from time to time, comparatively poor quality sites are pushed down in the search engine results. This happens during each update.

How the search engines understand that whether a site should be banned is a matter of controversy and those changes from time to time. Today a methodology may be ok, but tomorrow (in the next update) it may be considered unethical.

During the latest shuffle of the Google results, inorder to retain the quality of their search results, it has adapted a strict attitude against those trying to manipulate PR values of their sites or misuse the advantage of having a high PR.

You may heard of an ad network company, SearchKing. Their concept was to place text ads on sites that have a high PR score and use that PR as a way to gauge part of the value of the ad. An ad from a page with a PageRank of 7 cost more than an ad from one that had a PageRank of 6.

But, there was another effect of this network in Google's pagerank analysis system. When a site with high PR links to a site with low PR, a part of the importance is passed along to the site with low PR. Now when a high PR site feels another site worthy to link at because of the content, it is alright as it is the natural way to build PR. But in this case they were linking to poor quality sites against a payment and as a result in Google PR analysis, those sites were deemed as important one.

It was possible that after a certain period of time those not-so-worthy sites would have started to attain top ranks in the results, finally affecting the quality of the Google results. If they allowed this company get special treatment, the search results would get so messed up that they'd totally lose their relevancy after sometime. It was a threat to Google's successful business model.

Obviously, Google penalized the sites. SearchKing, the ad network site got a PageRank Zero penalty in the latest Google update. The main pages of the network of all hosted sites saw its PageRank reduced to half. These were the pages that had a high PR.

Their problem was that they were trying to sell and pass on the advantage of having a high PR to sites that may not be worth getting that importance.