Disable "CHANGE USER" on WIN7?HEEEELP!

Euskadi

Hi all,does anyone know how to disable this function on WIN7,I find it really annoying that after a while leaving my computer ¡dle,I have to clickthe icon(goldfish,flower etc) on the change user screen,BUT WORST OF ALL is whatever application is running at that moment stops and that can be really annoying leaving your PC doing something for a few hours while you go away and do something else only to arrive back to find the thing stopped after 20 minutes(like I did 5 hours ago, AAAAAAARGH)
Internet says doing this is a security risk and its not really clear how disabling is done

Any Ideas?
euskadi

mp22

turn off any screen saver,go into the power options and select never for all options,have a look here for locking you desktop when you are away from it
http://malektips.com/lock-desktop-windows-7-taskbarp.html