In order to gain access to XP systems where logon is required, only two key pieces of information are required – a valid username, and the password associated with that account. By default, Windows XP is configured such that the name of the last user to have logged on to the system appears automatically in the Log On to Windows dialog box. In effect, this is inherently insecure, since it gives other users half the information they require to log on to the system.
For a higher degree of security, Windows XP can be configured to not display the name of the last user that logged on to the system in the username text box. This is an especially useful feature on systems used by multiple users, since many people won’t even bother to look at the username text box during logon, and will attempt to enter their password only, resulting in a failed logon attempt. Whether the last username is displayed can again be controlled with a simple registry tweak. To stop the last username from being displayed, open Regedit and browse to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\
System and HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\
System and create a new REG_DWORD value in each called DontDisplayLastUserName. A value of 0 will display the name of the last user to log on to the system, while 1 will hide it.