Gmail is a free, advertising-supported email service provided by Google. Users may access Gmail as secure webmail, as well as via POP3 or IMAP4 protocols. Gmail initially started as an invitation-only beta release on April 1, 2004 and it became available to the general public on February 7, 2007, though still in beta status at that time. The service was upgraded from beta status on July 7, 2009, along with the rest of the Google Apps suite. With an initial storage capacity offer of 1 GB per user, Gmail significantly increased the webmail standard for free storage from the 2 to 4 MB its competitors such as Hotmail offered at that time. Individual Gmail messages, including attachments, may be up to 25 MB. Gmail has a search-oriented interface and a “conversation view” similar to an Internet forum. Gmail is noted by web developers for its pioneering use of Ajax. Gmail runs on Google GFE/2.0 on Linux. , it was the most widely used web-based email provider with over 425 million active users worldwide. According to a 2014 estimate, 60% of mid-sized US companies were using Gmail. In May 2014, Gmail became the first app on the Google Play Store to hit one billion installations on Android devices.