A packed file regardless of the packer used can’t hurt your system. It needs to be unpacked and then run before it can do any damage.
Before it’s run, it’s intercepted by your anti virus program. At that point, you’ll be told if the file is infected.

when one goes to internet options via the extras menu in the browser, and chooses to delete temporary internet files, are [i]all[/i] temporary internet files actually deleted, or can it happen that some are left over?
Nothing in life is certain except death and taxes. ;D Welcome to the forum.