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Every network capable device has a unique MAC (media access control) address. In the most basic sense, a MAC address is a serial number that allows one networked device to identify and communicate with another. Normally, there is no reason to change your network card’s MAC address. Doing so may even cause problems if you happen to chose a number that is already in use by another device. However, there are some reasons you may want to change your MAC address:

1. To get past MAC address filtering on a router or firewall.
2. For sniffing other connections on the network.
3. To keep your “real” MAC address out of traffic and security logs.
4. To pull off a denial of service attack by assuming the MAC of the gateway.

There are also a slew of other reasons for needing to change your MAC address.

Here are two ways to do it in Windows 9x/XP/Vista:

Method 1: Windows has a built in way to change a network card’s MAC address. This method seems to work as well as the second method, but may not be available depending on your network card.

1. Go to Start->Settings->Control Panel and double click on Network and Dial-up Connections.

2. Right click on the NIC you want to change the MAC address and click on properties.

3. Under “General” tab, click on the “Configure” button

4. Click on “Advanced” tab

5. Under “Property section”, you should see an item called “Network Address” or “Locally Administered Address”, click on it.

6. On the right side, under “Value”, type in the New MAC address you want to assign to your NIC.  Usually this value is entered without the “-“ between the MAC address numbers.

7. Go to command prompt and type in “ipconfig /all” or “net config rdr” to verify the changes.  If the changes are not materialized, then use the second method.

8. If successful, reboot your systems.

Method 2: This method uses a freely available program to change your MAC address. This program should work on any modern Windows installation.

1. Download MACAddressChanger.exe and save it to a convenient location.
2. Double-click to run the program.
3. Choose the network card you want to change in the first drop down box.
4. Type a new MAC address into the second box. You can type it with or without dashes.
5. Press “Change MAC ID.”