Detection difference between x64 and x86

Norton Security | Norton Internet Security
1

Hello,

I like test av, so I change them often and I downloaded packages with malware.

 

I tested package with 98 malicous files and Norton 360 v4.0 on Windows 7 Professional x64 detected 33 threads.

When I do the same test on Windows 7 Professional x86, it detected 58 threads.

 

I updated virus definitions, changed all settings to maximum and aggresive (sonar aggresive, heuristics to maximum, full scan) and repeated the test on 64 bit platform - it detected 35 threads...

 

It's unormal - Norton 360 (and probably NIS and NAV) in 64-bit system is less effective than in 32-bit...

Tests on other packages confirm this problem.

2

Is it possible that not all of the malware is detected because some simply can't run on 64 bit?  If it can't run, heuristics can't detect it.