A patent-holding company that already won a $200 million patent settlement from Microsoft in 2010 is going after the software giant again. Yesterday, VirnetX filed suit in the East Texas judicial district that it favors, seeking another patent win against Redmond.

This new lawsuit (PDF) asserts six patents that are alleged to cover Skype (which Microsoft purchased in 2011) as well as Microsoft products that may integrate Skype, like Lync, Microsoft's instant-messaging platform. The suit says the infringement is willful because Microsoft should have known about these patents due to VirnetX's earlier lawsuit and the license agreement it ultimately struck.

A March 2010 jury trial against Microsoft resulted in a $105.7 million verdict, and VirnetX was asking for an injunction as well. Two months after the verdict, Microsoft settled the litigation for $200 million. But VirnetX now notes that the license "was explicitly limited in scope, and Microsoft is not licensed to practice VirnetX's technology in certain excluded ways, particularly across non-Windows platforms."

VirnetX gets all its income from licensing patents. So although it talks about offering services, the company generally meets the standard of do-nothing patent-holding companies often called "patent trolls." The publicly traded company has 14 employees, and its corporate headquarters is a suite in a small office building in Zephyr Cove, Nevada, which it leases for $5 per month.

The company is experiencing an up-and-down year in the courts so far. In November, it won a $368 million verdict against Apple—and then immediately filed another lawsuit against Apple. That case has resulted in Apple changing how iOS devices use VPN. In a more recent case against Cisco, VirnetX lost, and its stock has gone down nearly 50 percent since then.