I've read many articles about how unnecessary or even bad it is to have more than one AV on your computer, is there any truth to it or it's just AV giants trying to scare their clients off competitors? The more AV programs you install the more resources you consume but apart from RAM/CPU usage, does having more than one real-time protection software have any real disadvantages? Can I have 3 or 4 AVs (Avast free, Qihoo, ESET, MBAM) and keep changing their configuration so I can have only one or two as real-time protection at a time?