Why does Spybot find trojans Norton 360 missed?

Amonetize.InstallPath

Win32.Downloader.gen

iCrossRider

Oscardelta.toolbar

SweetIM

Wajam

AllMyWeb.Toolbar

and a trojan called "OtShot"

were found by a free Spybot scan on my Norton 360 protected computer.  Needless to say, I'm NOT a happy camper!

I have paid Symantec good money over all these years for "protection".  What gives?  Spybot says this is serious.  All the other trackercrap we have to accept, I suppose, to get content.  What's the trigger for "OtShot" and how do you get rid of it?  N360 runs continuously.