Many practices that Google penalizes websites for using are referred to as "black hat SEO." This means those activities should be avoided at all costs because they'll hurt search result rankings despite the fact they superficially appear to fit the criteria for Google's search model rather well.
Some prior actions have been addressed by Google, and join the list of things to never even think about doing. The latest is the use of link networks, which are basically groups of websites that provide each other with mutual hyperlinks and lists of high-ranking pages that will ostensibly help with a company's SEO marketing strategy.
Google realized such sites weren't actually contributing to the value of the internet and have been deindexing sites that fail to fill this role. BuildMyRank.com, for instance, is the latest casualty in this fight as it recently ceased operations after being deindexed, according to Search Engine Land.
The good news in this situation is that Google has continued to make it clear what criteria will determine if a page can be considered useful to consumers and worth ranking highly – good content. As the inclusion of high-quality content is necessary for lead generation, there's no reason to attempt shortcuts like link networks and other black hat tactics.