The company was founded by Larry Page and Sergey Brin while both attended Stanford University. Together, Brin and Page own about 16 percent of the company's stake. Google was first incorporated as a privately held company on September 4, 1998, and its initial public offering followed on August 19, 2004. The company's mission statement from the outset was “to organize the world's information and make it universally accessible and useful”, and the company's unofficial slogan is “Don't be evil”. In 2006, the company moved to its current headquarters in Mountain View, California. Rapid growth since incorporation has triggered a chain of products, acquisitions, and partnerships beyond the company's core web search engine. The company offers online productivity software including email, an office suite, and social networking. Google's products extend to the desktop as well, with applications for web browsing, organizing & editing photos, and instant messaging. Google leads the development of the Android mobile operating system, as well as the Google Chrome OS browser-only operating system, found on specialized netbooks called Chromebooks. Google has been estimated to run over one million servers in data centers around the world, and process over one billion search requests and about twenty-four petabytes of user-generated data every day. As of September 2009 Alexa listed the main U.S.-focused google.com site as the Internet's most visited website, and numerous international Google sites as being in the top hundred, as well as several other Google-owned sites such as YouTube, Blogger and Orkut. Google also ranks number two in the BrandZ brand equity database. The dominant market position of Google's services has led to criticism of the company over issues including privacy, copyright, and censorship.