If i already have Norton antivirus will using avast as well do more harm than good?

use only one... using 2 or more will interfer with each other and possibly kill each other... same goes for fire walls..

think math... negatives and negatives cancel out...

firewall with another firewalll... might shut them both off completely

same goes for virus protectors

Now as for spyware, malware, and Ad-aware, you can have multiple ones.. they wont interfer with each other

If i already have Norton antivirus will using avast as well do more harm than good?systemworks

Well you can only have one or the other. I use avast because norton still cannot get rid of most viruses that avast can. PLus avast doesnt use as much processing like Norton.

If i already have Norton antivirus will using avast as well do more harm than good?windows

Having 2 anti virus in your system is not recommended. It may cause conflicts between them. It will just consume system resources. Plus you are not doubling your protection.
you at least must have one anti virus. when avast combine with Norton, they go crazy! i suggest you use avast instead of Norton. i know avast well because i'm a programmer. i have try avast and it is much more better than Norton.