It seems Intelligent skip scanning only scan certain files:
When Intelligent Skip Scanning is on, Norton Internet Security does not scan some of the common non-container files types that are available on your disk. The commonly available non-container file that Norton Internet Security skips are .dll, .gif, .png, .jpg, .asf, .avi, .bmp, .htm, .ini, .css, .cur, .fon, .ico, .inf, .sys, .ttf, and .wav.
What if the virus is hiding in the .dll and .inf and .ico files? Skipping those files won't give a "full" result.
Can someone explain more about Intelligent Skip scanning and when it will and will not apply.