Why can not the computer, install multiple anti-virus software?

I manage to install three anti-virus, AVG, AVAST, and AVIRA. Well its is not recommended to use more than one anti-virus because it will slow down your computer, because these anti-viruses will crawl your computer at the same time. There are anti-virus that do not allow to install until you remove the one that installed, like norton anti-virus, you cannot install this norton because its already programmed in norton not to install if there is another anti-virus in your computer. But if you know what is inside your computer you can avoid confusion, like the AVIRA, the AVIRA always popup saying detecting virus, but its my AVAST so I know its not a virus, because some anti-virus has programmed the other anti-virus in there data base that its a virus but not. If you install PANDA anti-virus, the AVG, AVAST Will say its a TROJAN VIRUS but actually not, because its already programmed that its a virus even not, because ANTI-VIRUSES is a business they don't want you buy other anti-virus, they want you to buy only their own product.

Still we can install more than one anti virus software in a computer and this depends upon the software we are going to install.Some of the software requires disabling the previous software before installing the new.I don't find anything important to prevent us from installing the other anti virus software when we have one more already, other than business competition among the anti virus software vendors.But installing more software slowdown our system to great level though we have better virus removal.

Usually only one antivirus is allowed. During installation, the antivirus checks for presence of another antivirus and usually won't install until the older AV is removed. However, I did manage to install both Avast and AVG once. One trick you can do is install both antiviruses but use only one at a time (you can manage from the settings/preferences). Then you can use one AV for one week and another for the next. Make sure both AVs are up to date. And if you feel really paranoid about it, install Linux. I did that and feel really safe!