Following today's December NPD U.S. retail game results, Microsoft said Xbox 360's worldwide install base increased to 39 million units since its 2005 launch. It made the announcement after selling 1.3 million U.S. units in December and 10 million U.S. sales in 2009 overall, as the system maintained a software tie ratio of 8.8 games sold for each console. The console had "more titles in the list of monthly top ten consoles games throughout the year," Microsoft noted -- as opposed to the total top 10 list of 2009 bestsellers, which was heavily dominated by Nintendo. Microsoft also said its system generated $4.8 billion in revenue in 2009, down slightly from $5.0 billion in 2008 and $5.1 billion the year before. For third-party game sales, however, the brand remains extremely strong, generating $2.4 billion, or 43 percent of the industry's third-party game revenues in 2009. Online service Xbox Live hit its highest concurrent user count in 2009, reaching 2.2 million people simultaneously. Mentioning Natal as well as upcoming games like Mass Effect 2, Splinter Cell Conviction, and Halo Reach, Microsoft stated its belief that 2010 will be "the biggest and best year in Xbox history."