Every copy of Microsoft Windows XP Home Edition includes a very well hidden Administrator account. In normal use, you will never see this account. About the only time it shows up is if you bring up the computer in a special state called Safe Mode, which usually occurs only after a serious system problem. But the Administrator account is there, and someone who has physical access to your PC and knows a couple of tricks can use it to gain access to any information on your computer, including data in files that you think are password-protected. And while you may think that your computer is safe from prying eyes in your home or small office, this is not always a sound assumption, especially if there are technology-savvy teenagers around.
Here's how to close that hole:
1. Go to the Start menu, and click Run.
2. In the window that opens, type "control userpasswords2" without the quotes, and click the OK button.
3. A new window will open listing Administrator and any other accounts you have set up on the machine. Click on Administrator to highlight it, and then click the Reset Password button.
4. Enter the new password in the boxes marked "new password" and "confirm new password" and click OK.
5. Click OK to close the User Accounts window.
By doing this, you will have lost an emergency back door into your computer that could be used if you ever forget the password to your user account. Fortunately, there's a much better way to deal with the problem -- one of the few remaining uses I know of for a floppy disk.
From the Start menu, click on Control Panel, and then double-click User Accounts to open it. Click on your own account. In the window that opens, find the link in the upper-left corner labeled "prevent a forgotten password." Follow the instructions in the Forgotten Password Wizard that will open automatically.
Put the disk in a safe place. If you ever forget both your own account password and the passward you created for the administrator account, you can put this floppy in the drive and use it as a sort of master key to gain access to you computer.
The password-reset disk option is not available on Windows XP Profession Edition computers that are part of a corporate network.