Although physical MAC addresses are permanent by design, several mechanisms allow modification, or "spoofing", of the MAC address that is reported by the operating system. This can be useful for privacy reasons, for instance when connecting to a Wi-Fi hotspot, or to ensure interoperability. Some Internet service providers bind their service to a specific MAC address; if the user then changes their network card or intends to install a router, the service won't work anymore. Changing the MAC address of the new interface will solve the problem. Similarly, some software licenses are bound to a specific MAC address. Changing the MAC address in this way is not permanent: after a reboot, it will revert to the MAC address physically stored in the card.
Other methods of changing the MAC address are permanent; at least one network card manufacturer bundles networking hardware with software that allows the user to change the MAC address. These network cards usually come with a bootable CD-ROM that executes a utility that permits the user to change the MAC address burned into the EEPROM. When a hardware-based solution is not utilized, the user who intends to change the MAC address must instead rely on a software-based solution. The appropriate software solution is dependent on the operating system installed on the computer. Various software-based solutions are described below.
As a MAC address can be changed, it can be unwise to rely on this as a single method of authentication. IEEE.1x is a standard better suited to authenticating devices at a low level.