System Works Did Not Detect W32/autorun-KO

Can anyone help in regards to this?

 

I had to run Bit-Defender to clean the virus off of the computer, as everytime I ran Nortons it would knock it off because of the operation platform being windows.

 

Does anyone know why Nortons System Works did not detect the virus?  I have used Nortons for years and never had a problem until now.

 

Thanks for any input.