Of the five biggest tech companies in the US, Microsoft is the only one that isn't currently in the crosshairs of US antitrust authorities. 

The software giant already took its turn through the regulatory wringer starting two decades ago, a years-long confrontation that resulted in the finding that the Redmond, Washington-based company had illegally maintained its monopoly for personal-computer operating-system software. The case dealt with the company's moves to kneecap the Netscape web browser by bundling its own product, Internet Explorer, into Windows, the dominant PC operating system.