The network security code, or WEP (wired equivalency protection), is a long series of letters and numbers that is required to be present on any computer attempting to access your wireless network. This will keep strange computers from attempting to steal your bandwidth, as it is unlikely these computers will be able to randomly guess the code. Finding the network security code will require access to the router settings, the wireless port to which your computers connect.
Look through the manual for your particular model of router. Contained within should be the IP (Internet protocol) address for your router. Input this address into your Internet browser to access your router's security settings. The address will typically be something like "http://xxx.xxx.x.x" with "x" indicating the different numbers unique to accessing your particular model.
Enter the default user name and password for the router, which should also be in the instruction manual. If you have lost the manual, you can often obtain an electronic copy online at the manufacturer's website. Most default router passwords are something along the lines of "username: admin," "password: admin" Thus, try inputting "admin" as both the username and the password if you are having trouble locating your manual.
Navigate to the "wireless security" option from the Options menu that will appear in your Internet browser. There you will find the network security code listed under the WEP settings. Write the code down and keep it in a safe place. You can change the code every month if you feel it necessary to prevent people from attaining access to your network through sheer luck and persistence.
The easiest and most secure method of changing your WEP password is to use the random "Generate Key" button present within the WEP settings on the wireless security page for your router's options. Change your router's settings to 128-bit encryption for a more secure home network, as the pass code will be longer than 64-bit encryption, making it harder to guess or hack into. This option should also be present on the WEP settings page within the router's options.
When copying down your WEP password for use on other computers in your home, be careful to distinguish between similar looking characters such as "1" (the numeral one), "I" (upper case "i") and "l" (lower case letter "L"). This will save you the time and frustration of having to go back and double- (or triple-) check the code while setting up the other computers on your network.