A new rumor has surfaced that suggests Microsoft is considering a third method for distributing copies of Windows 7: USB flash drives. We already know Microsoft plans to offer a retail version as well as a downloadable version of Windows 7, but these two options present some challenges for users with netbooks that lack DVD drives who want to upgrade to Windows 7. According to an undisclosed source, CNET claims “Microsoft is considering offering Windows 7 on a thumb drive to allow netbook owners to more easily