One anti-virus program or two?

[Legolas8181]

I have been told that you can have as many as you want installed but only one can be active at a given time otherwise they conflict with each other but then I heard from a friend of mine who claims that you can have 1-3 different programs but 2 being the sweet spot being active and claimed that a tutor in ICT at my College confirmed it as well but I never heard him say that. So which is it? I currently have Malware Fighter, Drivers Booster, ASC 7 and Smart Defrag 2.

 

[USAFRet]

One and only one active anti-virus at a time.