Once people started to figure out that backlinks produced the sound of a register being opened, they decided to set up multiple websites and interlace all of them with backlinks from each.
This is not the same as getting friends and neighbors to reference your site. What happens when you own the other sites is that they are inter-related links on multiple sites that you own and operate. While this had the desired effect of boosting your PageRank for a while, it was quickly listed as a black hat trick by search engines and penalized.
For one thing, the backlinks will mostly show up as reciprocal links from inter-related websites. For another thing, they will usually be tying into link farms and nothing more – no real content. This strategy might have worked in the past, during a small window of opportunity, now it will get you heavily penalized, if not sandboxed all together.
It doesn't take many mistakes to totally kill one of your top websites and get it taken out of the search engines altogether.
Be careful when you start your link campaign to make sure that your not overdoing it and they are not getting your links placed over sites that Google and Yahoo concert the link farms.
You can spend loads of time and effort building back links to your site and then make all that work absolutely useless by a few bad mistakes in your link building efforts.
Take the time to build quality back links it's well worth the extra work.
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