Early SEO practitioners quickly realised that links were an extremely powerful aspect within Google search, and that acquiring links had a significant impact on results. As the number of sites online increased dramatically, so did the number of those attempting to use links to increase their rankings.
This led to some marketers to adopt aggressive tactics to increase the numbers of links to their sites, including:
These aggressive tactics revealed that links were Google's "Achilles heel", leaving search rankings open to ready manipulation by those with sufficient resources. In response, Google has adopted increasingly aggressive tactics of its own to combat these practices. This includes:
How and when Google applies penalties and demotions is a complex topic - and beyond the scope of this guide. However, be aware that penalties applied by Google can have a substantial and long-lasting effect, in essence, preventing your site from ranking for your desired keywords for a considerable time.
Avoiding a perception of link spam is a critical factor when undertaking offsite SEO.