NIS2011 Failed Detection

NIS2011 failed where NIS2010 succeeded...?!?!

 

Here's the case:

I had enabled "Don't show hidden files, folders..." and "Hide protected os files" on my W7 Explorer.

I plugged in a USB drive without knowing it was infected.

I browsed the contents of the USB drive without NIS2011 giving any alarm.

I plugged it in to another computer with an AV product from another company.  It immediately announced it blocked the autorun.inf, and thus I was bewildered that I got an infected USB drive.

I then immediately ran a manual scan on the drive with NIS2011.... and found....

 

The W32.Harakit has been circulating around my local town for quite some time.  I remember with the same W7 Explorer settings, NIS2010 caught it as soon as I browse any infected USB drive.

 

Why is NIS2011 not picking it up upon browsing the drive concerned?  I identified the source of W32.Harakit, and I had successfully duplicated the problem with another USB drive.

 

Though I am certain my pc is not infected, I am really concerned that NIS2011 isn't doing its job as should be......