To require users to press CTRL+ALT+DELETE before logging on
You must be logged on as an administrator or a member of the Administrators group on a computer that is part of a network domain in order to complete this procedure. Network policy settings may also prevent you from completing this procedure.

Open User Accounts in Control Panel.
Click the Advanced tab.
In Secure logon, select the Require users to press Ctrl+Alt+Delete check box.
Notes

To open User Accounts, click Start, click Control Panel, and then double-click User Accounts.
Pressing CTRL+ALT+DELETE before logging on guarantees that the authentic Windows logon prompt appears. Requiring the use of CTRL+ALT+DELETE increases security and helps to thwart certain Trojan horse programs.
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