NIS can not kill Backdoor.Trojan etc?

On my PC with Vista Home Premium,
Windows updated all the time, 
have some Anti-Virus installed.

However, since last Friday, as soon as
connected to Internet, it will do very large
packets upload, 3.8 MB per minute, continuously,
used up my upload band width,
so that I can not do browsing, emailing, etc...

Yesterday, I installed Norton Internet Security 2009,
full system scanned, so I can do browsing, updating,
again.

NIS2009 record shows:
        Many repetitional Auto-Protect scanned, intercepted and solved high-risk activities,
        Backdoor.Trojan     W32.Popwin     Suspicious.MH690.A     W32.Mumawow.Flinf     Trojan.Dropper,
        file name C:\Winsows\temp\tmpxxxx.tmp.   
        No action.    Action for this activity not found.

NIS is great on block these malfunctions, however, why can't it find actions to kill them out right
and not let them activate again?

 

Thanks,

 

David