People change their IP address and thinks they are anonymous on internet but this is completely false you can trace down with the help of Mac(Media Access Control) address of your computer.Actually tracing is always done with the help of Mac Address.
Now the question arises how to change the mac address?
Then the solution is here although it sounds like practically impossible
but there exist an application known as SMAC :). It helps you in spoofing(changing) Mac Address maintain your anonymity on internet.
SMAC is a powerful, yet an easy-to-use and intuitive Windows MAC Address Modifying Utility (MAC Address spoofing) which allows users to change MAC address for almost any Network Interface Cards (NIC) on the Windows VISTA, XP, 2003, and 2000 systems, regardless of whether the manufacturers allow this option or not.
You can download SMAC here
SMAC does not change the hardware burned-in MAC addresses.SMAC changes the "software based" MAC addresses, and the new MAC addresses you change will sustain from reboots.SMAC helps people to protect their privacy by hiding their real MAC Addresses in the widely available wifi Wireless Network. SMAC also helps Network and IT Security professionals to troubleshoot network problems, test Intrusion Detection / Prevention Systems (IDS/IPS,) test Incident Response plans, build high-availability solutions, recover (MAC Address based) software licenses, and etc...
Please Share this information and stay tune for all new updates.