Looks a pretty nasty thing to me.
It all began with Google's aggressive attempts to curb link popularity manipulation by penalizing sites that purchase site- wide text link ads to get lots of incoming links in a hurry. (eg: If the ad selling site had 1,000 pages, the advertiser's link would instantly be on 1,000 pages.)
Google began filtering sites that indulged in this kind of linkage and either penalized or flat-out removed the site from its database. Bad news for that business. Excellent news for their competition. Can you guess what's coming next?
Certain scoundrels began thinking: "If buying site-wide text link ads en masse will get my site into hot water with Google, why not buy them for my competitor's site instead? Then just sit back and wait for Google to solve my number one business headache... the competition." (Cue evil laughter sound track.)
This, ladies and gentlemen, is Google Bowling. Simple. Devious. Devastating. And not just in theory; it's really happening out there.
Source
Webpronews.com