All network adapters have an unique identifier assigned by the manufacturer known as Media Access Control address (MAC address), this MAC address is used to identify a particular device on a network and was intended as a globally unique identification numbering system to trace network activity and implement restrictions and security, MAC address are used by many ISP's worldover for binding network access to a particular modem, however this MAC number can be changed easily via readily available noob friendly MAC spoofing tools, here are few tricks and tools to spoof your MAC address on Windows, Linux and Apple Mac.
For spoofing MAC Address on Linux computers you will need to use following commands with MAC address of your choice:
# ifconfig eth0 down
# ifconfig eth0 hw ether 00:80:32:AA:c1:40
# ifconfig eth0 up
# ifconfig eth0 |grep HWaddr
For MAC Spoofing on Apple Mac computers follow the instructions provided here.