Ran limbo again: it got sandboxed! So, I go to avast settings, set AutoSandbox mode to 'ask' and run Limbo again. So, I added it to the list of files that will automatically be excluded from automatic sandboxing. First time I ran it, Avast picked it up because 'static analysis finds the file suspicious'. I purchased Limbo on Steam, and am trying to run the game.
I've run into my first severe problems with Avast today that got me really frustrated.