Under U.S. copyright law and the Digital Millennium Copyright Act, it is illegal to copy, distribute or install software in ways that the license prohibits. Software licenses are typically limited to a one time only installation.
Microsoft states in its license agreement that the user may transfer the software to a third party only with the licensed device, the Certificate of Authenticity label and the agreement itself. Prior to the transfer, that party must agree that the agreement applies to the transfer and use of the software. The user may not retain any copies. If the license is sold, he loses any rights to use the software. He must also remove it from all of the devices on which the original license allowed him to install it.