At different points in recent times, the maximum market capitalization of each of these companies has ranged from half a trillion to one trillion US dollars. As such, they have replaced the energy giants such as Exxon Mobil, BP, Gazprom, PetroChina and Royal Dutch Shell (the so-called "Big Oil") from the first decade of the 21st century at the top of the NASDAQ stock index. They have also outpaced the traditional big media companies such as Disney, AT&T, Comcast and 21st Century Fox (the so-called "Big Media") by a factor of 10. In 2017, the Big Five tech companies had a combined valuation of over $3.3 trillion, and made up more than 40 percent of the value of the Nasdaq 100 index. Among the Big Five, Google has monopolized the web-based functions of online search (Google search), online video sharing (YouTube) and online mapping-based navigation (Google Maps). Facebook and Google share a digital advertising duopoly. In addition to social networking, Facebook also dominates the functions of online image sharing (Instagram) and online messaging (Whatsapp). Amazon is a leader in e-commerce. Amazon is the leader in providing cloud services with nearly 50% market share. Apple sells high-margin smartphones and other computing devices. Amazon with 69% market share and Google with 25% market share, lead the charge in the area of Artificial Intelligence-based personal digital assistants or smart speakers (Amazon Echo and Google Home). There has been speculation that it may not be possible to live day to day in the digital world outside of the ecosystem created by the Big Five. Some have also raised the issue of regulating their influence in the areas of privacy, market power, free speech and censorship (including inappropriate content), and national security and law enforcement. On the other hand, by providing cheap or even free services to consumers, they remain popular.