When Office 2013 (part of Microsoft 365) initially shipped, the license policy stated it could only be installed on a single computer, and that license could not be transferred unless you could prove to Microsoft that the computer was replaced under warranty. Due to a lot of negative customer feedback, Micorosoft has changed this policy, and now allows transferring Office 2013 licenses from one computer to another every 90 days. You have to call Microsoft to transfer the license, and this policy change affects Windows and Macs versions of Office 2013, and also trickles down to Mac Office 2011.