In Windows 7 this key combination brings up Windows Security which gives access to options like task manager, lock computer, switch user, change password and log off.
But most people do not use many of these features; they mainly use this option to bring up task manger.Now you can enable or disable these unwanted option using Tweak CTRL+ALT+DEL Option Tool.
CTRL+ALT+DEL Option Tool is a portable freeware application. Just run it and choose the appropriate options that will appear in the CTRL+ALT+DEL menu screen. If you want to change the options you can do it any time just by altering the changes made.