Should I use two antivirus at the same time?

Dennis Faas's picture

Infopackets Reader 'gfaas' writes:

" Dear Dennis,

What is your opinion of having two antivirus programs installed instead of one? I have Microsoft Security Essentials and Grisoft AVG antivirus. "

My response:

In my opinion, using two antivirus / antimalware programs is better than one for the same reason you would seek the advice of two independent doctors for a life threatening illness. That said, I suggest that you ensure both antivirus / antimalware programs do not conflict with each other, or you will run into resource issues that will cause your computer to slow to a crawl. In other words, make sure that:

a) both programs are not set for real-time file scanning at the same time, and

b) both programs are not scheduled to do a full / quick scan at the same time

If you have both programs set for real-time file scanning, both programs will be fighting for the same resource at the same time. You may also likely have problems accessing files; for example, downloads may fail to completely download, become corrupt, or are inaccessible.

Microsoft Security Essentials vs Windows Defender

For the record, Microsoft Security Essentials (MSE) provides both antivirus and antimalware protection. It "runs on Windows XP, Windows Vista and Windows 7, but not on Windows 8." (Source: I believe that by default, MSE is a separate 'add on' for the operating system and must be downloaded manually.

Windows Defender provides only antimalware protection; it is "included with Windows Vista and Windows 7 and is available as a free download for Windows XP and Windows Server 2003." (Source:

In Windows 8, Windows Defender replaces MSE as it does both antimalware and antivirus. (Source:

If it's clear as mud, thank Microsoft for the confusion.

Enable or Disable Windows Defender Real-time Scanning

I don't use Microsoft Security Essentials, but I do run Windows Defender, as it is part of Windows 7. To illustrate how to avoid resource conflicting, I'll outline steps on how to disable real-time scanning in Windows Defender, as I also run Avast! antivirus (free) and it already has real-time antivirus scanning enabled.

To access Windows Defender, go to the Control Panel and search for "Windows Defender". Once launched, go to the Tools menu, then click the Options link, then on the left menu you'll see "real-time Protection"; click that, then uncheck mark 'Use real-time protection.'

The Second Opinion: Windows Defender Full System Scan

You will also want to schedule a full system scan instead of a Quick Scan. I believe by default a Quick Scan is enabled at 2AM (at least, it was on two of my Windows 7 machines). This is basically where you get the 'second opinion' when running two antivirus / antimalware programs, as one will provide real-time file protection, and another with a full system scan. The second opinion is essentially the difference in the way the programs are able to identify threats, due to the differences in the heuristics engine as well as antivirus / antimalware definitions. To make the changes, go to the Tools, Options, then click the Automatic Scanning menu, then change from Quick Scan to Full Scan.

Also ensure that your backups (if you have any) are not scheduled at the same time. Set them to run at least an hour or later.

Additional Support: Ask Dennis

If you need help with adjusting your antivirus and antimalware settings to ensure they are no conflicts (and to ensure your system is running at its optimal performance), feel free to contact me for help via the website contact form.

About the author: Dennis Faas is the owner and operator of With over 30 years of computing experience, Dennis' areas of expertise are a broad range and include PC hardware, Microsoft Windows, Linux, network administration, and virtualization. Dennis holds a Bachelors degree in Computer Science (1999) and has authored 6 books on the topics of MS Windows and PC Security. If you like the advice you received on this page, please up-vote / Like this page and share it with friends. For technical support inquiries, Dennis can be reached via Live chat online this site using the Zopim Chat service (currently located at the bottom left of the screen); optionally, you can contact Dennis through the website contact form.

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stekcapofni's picture

Yes. If you want to bring your system to its knees.

Dennis Faas's picture

As stated in the article, if you configure antivirus and antimalware to not conflict with each other, it's perfectly safe. If you don't know how to configure it, contact me using the contact form and I'll do it for you. Alternatively you can use to check a specific file against 40+ virus engines / definitions.

Sparkydog's picture

Use ESET NOD32 Antivirus and you will never go back.

Curt's picture

My company requires McAfee enterprise on all PCs connected to the network. This works well enough most of the time. However, recently I was infected with malware that forced all four of the processors on my system to run at 100% utilization almost all of the time. A full scan with McAfee did not find the issue. I was able to manually identify four rogue processes that were maxing out my system and terminate them. However, they would spontaneouly restart so I downloaded the free MalwareBytes trial version. MalwareBytes found 17 infected files and removed them. I did exactly what you recomended and set the two AV programs to scan at different times. I also excluded the directories where my VMware writes from montoring by either program (this sped up VMware sessions significantly). In short, at least these two AV programs coexit on my Win 7 64-bit system with no detectable loss in performance.