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This can be done by adding hyperlinks to comments in blogs and also to pages that can be edited openly without regard to topic relevance.
New methods of spamming continue developing as search engines are employing measures to spot pages that deal with this illicit activity and probably ban them from being indexed. Studies are also being undertaken to detect spam pages. This includes evaluation of webpage content, using a spam mass formula which initially determines if your page is associated with those classified as good or bad sites and other strategies too that are constantly changing to match the evolving spamming methods.
When it comes to outbound linking, as long as webmasters evaluate the pages they link out to and make sure that they are not associated with spamming activities, it increases page rank. Link wisely.