Your Personal Pass To Privacy.  

When more than one person shares the same computer, you can use separate user profiles to keep your information secure. In this way, the Desktop, display options, and MY DOCUMENTS folder will display the preferences of each specific user. To access your profile, simply enter your Windows private username and password each time the computer starts up. (Your Windows password is separate from your network password, the one you use to connect to the network, if you are part of one.)

To add a user profile, click the Start button; select Settings, Control Panel; and then double-click the Users icon. Step through the Enable Multi-User Settings Wizard and click Finish when you are done.

To change your Windows (or network) password, make sure you’re logged on to the system with the existing username and password. Double-click Passwords in the Control Panel to display the Passwords Properties dialog box. Click the Change Windows Password button in the Change Passwords tab to modify the password you use to display your settings for the Windows 98 Desktop. Click the Change Other Passwords button to revise your network password.

Access Manager - More info

     If the above options do not provide enough security for you, download Access manager for Windows.

Access manager provides much more security than standard ways in Windows.

More info

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