Here’s Black Hold SEO in reader’s digest terms:
1. Google takes away your link juice if you link off your site, so no outgoing links.
2. Get as many links to your site as possible from authority sites, sucking in all the link juice possible.
Here’s a couple of trusted black hatter blog posts that have more to share about black hole SEO:
http://www.bluehatseo.com/100s-of-linkshour-automated-introduction-to-black-hole-seo/
http://seoblackhat.com/2008/09/08/black-hole-seo/
And here’s the visual depiction to help you get the concept:

Notice how everything goes in: nothing comes out.
Google favors these kinds of sites. Sites that link off to others are quickly being outranked by those that don’t link. How does this work to your advantage?
Get all the links you can, as fast as you can, however you can.
How? Here’s one suggestion:
1. Sign up to as many social bookmarking sites as possible.
2. Create 10, 20, 500 accounts on each site. The sky is the limit.
3. Link to the pages of your sites from the accounts.
Get more and more and constantly more links. It’s really the best way to outrank.

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