Why You Shouldn’t Install Multiple Antivirus Programs on One PC

Do you have an antivirus installed and running on your system? In this day and age when free antiviruses can top the leaderboards on virus detection tests, there’s always a solid and efficient security solution you can download without spending a penny. This may get people thinking about downloading multiple antiviruses. After all, the more you download, the safer your computer will be, right?


Unfortunately, the concept of “the more the merrier” doesn’t work so well with antivirus! In fact. the more antivirus you install on your system, the messier it can get. It may sound weird – after all, it sounds better on paper to have multiple layers of security – but there are reasons why you don’t want to install multiple antivirus software at the same time.

Performance Problems

When antiviruses work on protecting your computer, they need to use computer resources in order to perform their job. Not only that, they have to keep tabs on every potential entry point that a virus can use on your computer. This can range from plugging in a USB stick to downloading a file from the Internet. As such, it needs to perform what’s called “real-time scanning” which monitors any actions being performed on files and checks to see if it’s a virus performing said action.

This is fine when you’ve installed just the one antivirus, as it has enough “room” to settle in and do its job. The more antivirus programs you add, however, the more memory gets taken up by antiviruses scanning every potential intrusion point. What this leads to is a computer which won’t have enough memory available to perform other tasks, so you’ll find it running slower than before.

Fighting Over Files

Even worse, you’ll find that they’ll often clash with one another when protecting your system. The goal of an antivirus is to work as quick as possible to isolate a virus when it infects your PC. This means that you’re going to have two or more highly vigilant antiviruses that will be monitoring everything you do at exactly the same time. While it initially sounds good, the results will be anything but!


Let’s say you download a file from the Internet. A good antivirus will pick up on this action and immediately perform a scan on said folder to make sure it’s not infected. Unfortunately, if you’ve downloaded several good antiviruses, it means they’ll all clamour over one another to scan the file all at once. You may find the file is deadlocked where every antivirus is trying to claim ownership of it, and you’ll probably notice a system performance decrease while this happens.

When a file does turn out to be a virus, multiple antiviruses can end up making things more trouble than need be. Both of them will want to remove and delete the virus under their own terms, which will cause both of them to ask you if you want to quarantine them. Unfortunately, they’ll only really accept a quarantine if they’re the ones doing the quarantining. If you allow one to quarantine the virus and deny the other one, that second antivirus may pick up on the file in the first antivirus’ quarantine and constantly alert you of a virus threat, despite the fact that it’s safely stored away!

Accusing One Another

The worst effect of multiple antiviruses working in tandem is that they won’t trust one another. When an antivirus does its job, it assumes it’s the only one installed. Therefore, if they detect a second antivirus scanning through files, they’ll assume it’s actually a virus. At best, you’ll be bombarded with false virus alerts when the antiviruses spot one another. At worst, they may begin trying to delete each other’s files which will lead to system instability and important files being corrupted.

What About Scanners?


Throughout this article we’ve been focusing entirely on antivirus programs – the ones that work in the background on a deep level in an operating system. You may have downloaded anti-malware and anti-spyware scanners to help protect your PC. These are different, as they aren’t always scanning for threats but can be used to do a single sweeping scan on a PC when you ask it to. Will these scanners cause trouble with an active antivirus?

To answer this, it depends on what you’re using the scanner for. Some scanners have their own real-time scanning option which will probably conflict with an antivirus’ own. If you disable these real-time features and perform a simple scan with it, it probably won’t conflict. Ideally, you can tell your antivirus to exclude the scanner from its own scans, so it’ll leave your scanner alone. Even then, however, you may notice a performance drop as both of the software scan at the same time.

If you’re interested in using an antivirus and a scanner at the same time and want to learn the ramifications, look on the website of your favourite scanner software for help. For example, Malwarebytes has a list of compatible antiviruses (PDF) while Spybot discusses how to make it work hand-in-hand with an antivirus.

All for One

When researching antivirus software, you may feel tempted to download and run multiple programs to boost your security. The truth is, this is far from ideal! Pick one antivirus you gel with the most and use that one alone. If you want to secure your computer as much as possible, read antivirus reviews and pick the one that performs best.

What does your computer’s security look like? Do you make use of an active antivirus and scanners? Do you use your OS’s built-in antivirus solution? Or are you using an OS that doesn’t need one? Let us know below.

Simon Batt Simon Batt

Simon Batt is a Computer Science graduate with a passion for cybersecurity.


  1. Windows 10 has Windows Defender, a built-in antivirus program. Does this mean that I should not install Norton Internet Security Suite on my computer? And is one better than another? I’m a little confused on that matter.

    1. Hi Jathan! I understand your confusion; after all, Windows Defender isn’t something you can simply uninstall from your machine. If you’d like to install Norton on your system, just make sure that your Windows Defender is disabled after you install it. Sometimes antiviruses will automatically tell Windows Defender to turn off after they’re installed, so you may not even have to worry! After Windows Defender is disabled, it won’t be performing real-time scanning on your system, so Norton can do its job.

      As for which is better than which, it can be an opinionated topic! If you’d like something based on actual antivirus tests, I like to compare antiviruses using the website AV Test. Windows Defender scored 3.0/6.0 for protection, 4.5/6.0 for performance and 5.5/6.0 on usability. Norton scored 6.0 across the board, except for usability, which was a 5.0. In terms of keeping your PC safe, Norton would be a better choice from these results alone!

      1. Simon,

        You’re awesome! Thanks so much for all the great information. This is why I like this website so much. Practical, real-world advice that is actually helpful. Thank you so much!


      2. Precisely. And that is why one CAN install multiple antiviruses on a computer. But, ensure that one is active and others are not. Then you can do a switch to one of the non-active AV’s and deactivate your normally active one. This process gives you the best options. I’ve had files on my computer which were years old, sitting there not being used and suddenly AVG announces that they have malware/viruses in them. WTF? After 10 or so years it “finds” virii in files I’ve had for years???

        Switching to another AV in some cases shows they are clean, in other cases they see some that are infected. So, at the end of the day AV’s are only as good as their particular definitions database.

  2. I don’t use any antivirus for the past 6 years because it does more harm then good:

    – Always makes your system slower
    – Regularly blocks legitimate programs and files (worldwide regularly Windows systems are destroyed by a virus scanner)
    – Stupid/unnecessary questions (you like to allow rundll.dll? you like to update? you like to upgrade?)
    – Spam (every year ‘you have to upgrade for $$$’ announcement)
    – Regularly destroys the internet connection
    – Virus scanners are a palliative, preventative measures are much more important and smarter. Creates false sense of security, while it is not a preventive measure.
    – Virus scanners have many unnecessary junk such as a firewall (everyone already has a firewall of the OS + hardware firewall/NAT on the modem/router)
    – Wear of the hardware (through daily scans… Your data becomes less secure by this)
    – Screen pollution by extra buttons, toolbars sys icons
    – Personally I have nothing but inky experiences with all brands of scanners, except for Microsoft Security Essentials. That it detects less does not matter to me, it detects the major virus outbreaks very well (better than the big brands), and it prevents: blacklist of websites, uninstalling Adobe/Java, stops all kinds of advertising, etc.

    1. IOW, what you are saying is that all the cyber security experts are wrong and you are right?

      OH BOY! Are YOU misinformed!

    2. Marc,
      I cannot agree to just about all of what you write….ok the system will slow down slightly due to background scans and checks.
      I think this , thought, your entry is of a provocative nature ;-)

  3. I learned to not have multiple Anti-Virus programs running on my PC, years ago. I also learned that it isn’t always easy to remove these programs since they can be deeply embedded in the registry. I think all newbies(new computer users) try to do this since AVs have been around. I know that I did as a newbie. :O)

    Just one suggestion: If you find yourself still having elements of parts of the AVs, try using a program like Revo Uninstaller. There is a FREE version and it does extremely well. There are other Uninstaller programs that work wonderfully. I personally like using Revo Uninstaller. I have used that program for years and feel very comfortable using it. When I first started using Revo it was the FREE version and it simply cleared out a program. Revo is about 100% better than MS’s Add and Remove because it really does remove the registry stuff.

    Another thing – Before removing any AV programs check out their websites. Some of them have their own removable program and that is the only way their programs can be removed properly. Yes, I have had to use those removals to achieve my goal. I have learned to check out their websites before I start any removal process.

  4. Should anyone decide to remove their Anti-Virus program(s) the first thing you really need to do is check out the program’s website. There are a few AVs that have their own removal program and you can only get it from their website. If there is no website removal program then go ahead with the removal. I do suggest using a program like Revo Uninstaller, there is a FREE version and it works extremely well.

    Why use an uninstaller program? AVs are created to scan deep into your computer’s registry. Many elements of the AV are embedded in the registry, like all programs and needs to be removed. Uninstallers were created to remove elements in the registry. I started using Uninstallers when it became apparent that MS’s Add & Remove program was not good at removing many elements of any program in the registry. Mind you, I made my decision when I was still using Win XP.

    1. “MS’s Add & Remove program was not good at removing many elements of any program”
      For the most part, Add/Remove hides programs rather than removing them.

      Have you ever examined your Registry AFTER removing a program? If you do a search on the program name, you will still find Registry keys that contain it. They need to be removed manually which is not for newbies or the faint of heart.

  5. Never knew that about Multiple Anti-Virus Programs! Now, I do because; even though I have Paid for one of the top Ten Anti-Virus Programs with NO Complaints, I was going to get one of those ”Free Anti-Virus Programs”! Now I won’t!
    Thanks again for the Information,
    Thomas Orrow

  6. Since I use Linux, I on;y run my ClamAV every now and then, because of all the other measures I take to protect my system (iptables, SELinux, gufw etc.) I don’t find myself getting infected often, ….as a matter of fact,…..since installing Fedora Linux in 2004/’05?….I’ve NEVER gotten infected!…LoL! Guess its my diligent actions as well? (changing passwords every 3 months / 6 months) So I guess for me….trying to install anything more regarding security is almost counter-productive……since my desktop runs lightning fast…..(due to the 32GB of RAM and the 1TB HDD!…LoL!) To each their own though…

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