Linux is an open-source operating system. Open source means that the code for the software is generally available for modification by the developer community worldwide. In fact, this group development effort is what moved Linux from a few hundred lines of code to the robust operating system it is today, giving Windows and NT a run for their money. Red Hat Linux has become the leading version of Linux in the United States with over 75% of the market share. The entire Linux market is estimated to be approximately 10 million users, and growing daily.