Security startup Illumio said today that Microsoft chairman John W. Thompson has taken a seat on the Illumio board. Thompson is also CEO of Virtual Instruments and the former CEO of Symantec, so it’s clear the man knows a thing or two about the security and virtualization space. The new addition to Illumio’s board highlights the momentum the startup seems to be gaining in the competitive security market. The startup, whose technology focuses on securing enterprise workloads in the cloud or on premise, exited stealth in late October and has Morgan Stanley, Plantronics and Yahoo as clients. So far, it’s raised $42.5 million from Andreessen Horowitz, General Catalyst, Formation 8, Data Collective, Marc Benioff and Jerry Yang.