In the post-Penguin world, these links from unrelated sites only became a problem when they composed an exceedingly high percentage of a site’s total backlink portfolio. It should be no surprise that sites that had no links from authority or relevant sites faired the worst and received stiffer penalties.
The mitigating factor for pages that have links coming from non-related sites is that they have a material percentage of links from relevant and related sources as well. While Google doesn’t release specifics on their algorithm updates, it appears that the percentage of links sourced from relevant sites should be in excess of 10% of the total of inbound links.
Getting to even this minimum level of quality links is no easy task, which is a key point of the Penguin algorithm update. In this environment, shortcuts to success are vanishing; leaving a short list of activities that will deliver results. Of those activities, the most important activity is to generate high value content that readers will want to re-post and that authority and industry sites will want to link to. These alone will generate traffic and naturally build a link profile that will score points inside the algorithms used by the search engines.