Fast User Switching is a feature that allows multiple users to log into Windows and switch between accounts without logging off. When Fast User Switching is enabled, a "Users" tab will appear in the Task Manager, allowing the active user to control another user's session. The active user can send a message to the other user, connect or disconnect that user from the Internet or log that user off the machine.
If you want to prevent the active user from controlling other users logged in on the machine, you can disable Fast User Switching and remove the "Users" tab. To disable Fast User Switching you must have Windows 7 Ultimate or Windows 7 Enterprise.
Log into Windows as an administrator. Click "Start." Enter "gpedit.msc" into the search box. Press "Enter" to open the Local Group Policy Editor.
Navigate through the folders "Local Computer Policy," "Computer Configuration," "Administrative Templates" and "System." Click the "Logon" folder.
Double-click "Hide Entry Points for Fast User Switching" from the right pane. Select the radio button next to "Disabled."
Click "OK" to disable the "Users" tab in Task Manager.