Anti-Theft : "enable installation of Non-Market apps ..."

Avast Mobile Apps Avast Anti-Theft for Android
1

So sorry,
I am unable to go ahead with Anti Theft Setup, because
I cannot find the button, or the tic-box in my System Settings :
“enable installation of Non-Market apps …”

  • Android Built Firmware 2.2.1 for Motorola A1680
    and your application :
  • Avast 1.0.2129
    Can you enlighten troubled view please
    thank you, Maotouying
2

The Tickbox is in “Settings” → “Applications” → “Unknown Sources”
… Sorry for that …