Link spam has been around for about as long as Google has been using links as a ranking signal. In the early days of Google, black hat SEOs would use blog comments to pass high PR links back to their sites. Then in 2005, Google introduced the “NoFollow” attribute. Any link tagged with a “NoFollow” would be essentially invisible to search engines. The link was still active, but the attribute would make it so the link juice didn’t flow from one site to another.
Back in 2012, Google rolled out the now infamous Penguin update, which targeted sites that were using manipulative link building tactics to boost search engine rankings. Prior to the Penguin update, link building was relatively easy to game. SEOs used a combination of paid links, link networks, guest blogging, broken link building, press releases and blog networks to push their sites to the top of search results. However since then, many SEOs have put link building on a back burner to avoid potential penalties.
Lately there’s been a lot of speculation in the SEO community as to whether or not Google will continue to use back-links to rank websites and what metrics may soon replace links as a primary ranking factor. In Google’s latest webmaster video (below) Matt Cutts discusses how Google will value links going forward and how much of a role they will play in search engine rankings.