To further the above reply/info, if you open the interface, and select "scan", at the bottom of each scan area pane (quick, full, boot, and custom) is a settings button. (Some settings can not be modified in the free version).
Under "packers" , you will see and example of the types of files that will not be examined.
Such packed files are inert until unpacked and run.
At that point, if malware was detected, the file system resident shield would catch it.