Its always a good idea to lock your computer screen when you walk away. Here are a few ways to do this :

  1. windows key + L
  2. control + alt + Delete  then click lock computer (if you are bound to a domain)
  3. R-click on your background and choose properties. > click on the screensaver tab > hit the checkbox for the requirement of a password to take the computer out of a screensaver. > Set the idle time before the screensaver turns on