Norton has not detected some threats

Norton has not detected some threats as of the following:
Recently I connected an external hard disk to my lappie and scanned (as I was sure of malwares in it).
I could detect only just two threats and log showed as following:
On demand scan results:

  • Task name: On demand Scan
  • Files and directories:63,067
  • Reg entry, Process, Start up, Skipped, Trusted, Other Files: 0

Total Security Risks Detected & Resolved:

  • Heuristic Virus Res.:1
  • Security Risk Res.:1

Details from log:

  • webcakedesktop.exe
  • Threat name: WebCake
  • desktop.os.dll
  • Threat name: Trojan.Gen.3

But after resolving threats, when scanned with ZoneAlarm Firewall + Antivirus Free (It is my second line of defence) I could detect the following more:

  • delta.xul not-a-virus:Adware.Win32.DelBar.c
  • Backup files 1.zip not-a-virus:Adware.Win32.DelBar.c
  • SONY_SOUND_FORGE_&_>_KEYGEN.exe not-a-virus:Adware.Win32.Lyckriks.cw
  • Backup files 2.zip not-a-virus:Adware.Win32.Lyckriks.cw

Can I get any justification over this (as I had set norton to detect all those sort of stuffs):smileysad:. It seems NIS21.1.0.18 is up-to-date but is lesser effective than a free ver. AV ? :-(