Sandbox is a "isolation" program... As a sandbox is keeps all the sand (programs) in and excludes anything else from it and out of it. Sandboxie excludes any programs from many any changes from your hard drive... Meaning that if you start your internet browser with sandboxie, a virus will not be able to change/install from your hard drive. This also applies to any download you have done while you in sandboxie, so you have to allow them to install and such