YouTube is an American video-sharing website headquartered in San Bruno, California, United States. The service was created by three former PayPal employees in February 2005. In November 2006, it was bought by Google for US$1.65 billion. YouTube now operates as one of Google's subsidiaries. The site allows users to upload, view, rate, share, and comment on videos, and it makes use of WebM, H.264/MPEG-4 AVC, and Adobe Flash Video technology to display a wide variety of user-generated and corporate media videos. Available content includes video clips, TV show clips, music videos, audio recordings, movie trailers, and other content such as video blogging, short original videos, and educational videos. Most of the content on YouTube has been uploaded by individuals, but media corporations including CBS, the BBC, Vevo, Hulu, and other organizations offer some of their material via YouTube, as part of the YouTube partnership program. Unregistered users can watch videos on the site, but registered users are permitted to upload an unlimited number of videos and add comments to videos. Videos deemed potentially offensive are available only to registered users affirming themselves to be at least 18 years old. In July 2016, the website was ranked as the second most popular site by Alexa Internet, a web traffic analysis company. YouTube earns advertising revenue from Google AdSense, a program which targets ads according to site content and audience. The vast majority of its videos are free to view, but there are exceptions, including subscription-based premium channels, film rentals, as well as YouTube Red, a subscription service offering ad-free access to the website and access to exclusive content made in partnership with existing users.