Microsoft Corp. today announced that John W. Thompson, chief executive officer of privately held Virtual Instruments and former chairman and CEO of Symantec Corp., was appointed to the company’s board of directors, returning the board’s size to 10 members.

Thompson currently serves as CEO of Virtual Instruments, a privately held company located in San Jose, Calif., whose products are designed to ensure the performance and availability of applications deployed in virtualized and private cloud computing environments. Since 2009, Thompson has been an active investor in early-stage technology companies in Silicon Valley.

Thompson served as chairman and CEO of Symantec Corp., helping transform Symantec into a leader in security, storage and systems management solutions. During his 10-year tenure as CEO from 1999 to 2009, Symantec’s revenues grew from $632 million to $6.2 billion, and its worldwide workforce grew to more than 17,500 employees. Thompson stepped down as CEO of Symantec in 2009, and stepped down from Symantec’s board of directors in 2011.

Previously, Thompson held a number of leadership positions at IBM, including sales, marketing, software development and general manager of IBM Americas. He was a member of IBM’s Worldwide Management Council.

Thompson currently serves on the board of United Parcel Service, and he has served on a number of government boards and commissions, including the Financial Crisis Inquiry Commission, the National Infrastructure Advisory Committee, and the Silicon Valley Blue Ribbon Task Force on Aviation Security and Technology. He formerly served on the national board of Teach for America, an organization dedicated to eliminating educational inequities for all children.