Microsoft (MSFT) has sold 40 million licenses of its Windows 8 operating system after only one month of availability. Tami Reller, the company’s newly-promoted head of Windows, announced the news at the Credit Suisse 2012 Annual Technology Conference on Tuesday. The executive also revealed that Windows 8 is outpacing Windows 7 in terms of upgrades and that the company’s Windows Store launched with more first-day apps than any other app store. In fact, the size of the store has doubled since launch and “a number of apps” have even surpassed the $25,000 revenue mark. Microsoft’s latest operating system was launched last month with a massive $1.5 billion marketing campaign. Despite the large number of users upgrading to Windows 8, sales of Windows 8 PCs are said to be well below the company’s internal projections.