The media access control, or MAC, address is a globally unique identifier burned into network interface cards (NICs) by the hardware equipment manufacturer. It acts like the name for the machine on the network, so that it may be uniquely identified. It is also sometimes called a hardware address or physical address.
MAC addresses are 12-digit hexadecimal (base 16) numbers, 48 bits in length. They are generally represented as:
The first half of the MAC address (the M’s) is the "organizationally unique identifier" (OUI) and identifies the hardware manufacturer of the device. The second half of the address (the S’s) is assigned by the hardware manufacturer and can be allotted in any manner, as long as the addresses remain unique.
To find your computer's MAC address, for Windows, at the command prompt, enter ipconfig /all. For Linux, at the command prompt, enter ifconfig –a. For other operating systems, please refer to this Fermi National Accelerator Laboratory page .
The MAC address makes it easy to identify a network adapter anywhere in the world. This leads to the common belief that perpetrators of computer crime can be tracked using this "unique" identifier that has been physically burned into the network adapter. This is not the case, however, because there is free software with which you can spoof your MAC address by changing it to whatever you want. While this tool is designed to help in network troubleshooting, it can easily be used to hide the digital footprints of malicious users.