We all know that it isn't recommended to run more than one antivirus program at a time. But since Windows Defender comes with Windows, is it safe to have it and another antivirus program (AVG, Avast) installed and running together?

I imagine the answer may be different for Windows 7 and Windows 8, since Windows Defender in Windows 8 has more features and acts more like an actual antivirus program.

Thanks in advance!

  • It's counter productive but you can – Ramhound Sep 6 '14 at 1:44
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    @Ramhound : Why is it "counter productive"? It may seem redundant, but how does one program negate the effects of the other? The definition of "counterproductive" is something that is "not helpful : making the thing you want to happen less likely to happen". Did you mean "inefficient"? – sawdust Sep 6 '14 at 2:36
  • It's counter productive because if two programs attempt to deal with a single infection it's possible neither will fully remove it. It's also means two programs are scanning your files which is a CPU intensive task – Ramhound Sep 6 '14 at 2:41
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    If you're careful, which means no clicking on ads that ask you to download the so-called latest media player to view some video or to enable the Java web plugin, and no cracked OSes/applications, you'll be fine even without any AV. So just leave Windows Defender on and forget about it. – user256743 Sep 6 '14 at 9:25
  • It seems that now Windows 10 actually disables it's own protections anyway, if it discovers a third party that it recognises - such as this message on a work machine with Bit-Defender: "Windows Defender is not active because you're using other providers." – Hicsy Nov 17 '17 at 1:53

Recent versions of Windows Defender in Win7/Win8, being built into Windows, are explicitly compatible (thanks to changes made by other antivirus vendors, as well as changes made by Microsoft themselves) with most third-party virus scanners. That is, you won't see BSODs, etc. if you are using the latest version of Windows Defender combined with the latest version of any self-respecting antivirus program from a third party.

Your question was is it okay. Yes, it's okay. Your PC won't crash. It may run slower; it may run much slower -- but it'll work.

You will notice that, if you use certain websites that run your upload through 40+ virus scanners, almost every executable you can find will flag something in at least one virus scanner. On the other hand, actual viruses that are malicious will only be detected by some of the virus scanners, while not others.

If you were super paranoid, you could install numerous virus scanners and let them all do "on-access scanning" at once. This would drive CPU through the roof when doing writes to disk, and you would be getting loads of false positive results, but it'd work. Remember, although you marginally increase your chances of finding actual malicious programs by running more virus scanners, you also dramatically increase your chances of false positives. So you'll constantly be clicking on "shut up, it's okay!" dialog boxes and pop-ups. With 40 virus scanners it would be completely unmanageable.

However, TWO virus scanners is not unheard of. For example, you might run Windows Defender and Malwarebytes, or Norton and Kaspersky, or AVG and McAfee. It depends on which products you're invested in, which products you trust and which you don't, and how much you research on the internet to determine the reliability and business practices of each company, when you are selecting virus scanners.

The long story short is that currently, in 2014, the latest version of Windows Defender plus the latest version of "top tier" virus scanners (that is, ones which are widely regarded as actually good) do not conflict -- there are no compatibility issues whatsoever. This advice applies primarily to Windows 7 and later; I can't speak for the older OSes. But you will notice performance degradation if you run more than two virus scanners. For two itself, I don't think you'd really notice. I personally run Windows Defender and Malwarebytes.

Also note that some virus scanners may choose, as part of their installation program, to disable Windows Defender for you, assuming that their virus scanner is the only one you could possibly want. In that case, they are compatible, but you're only benefiting from the virus-scanning abilities of one scanner, not two.

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  • Techinically malwarebytes isn't a anti-virus it's a malware scanner. There is a massive difference between something let's say Flame/Cryptolocker and say "security suite 2014" malware – Ramhound Sep 6 '14 at 2:28
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    There's not a huge difference really, because the detection mechanism and steps taken to mitigate it are similar. Basically you detect it using some signature or heuristics, then you block it by preventing it from running. The only difference is the severity of the attack. Malwarebytes can find genuine viruses too, BTW. – allquixotic Sep 6 '14 at 2:31
  • I wouldn't know. I have never been infected because malwarebytes either blocks the download from a malicious host or blocks the website all together but I would argue there is some difference otherwise. I am pretty sure the main guy behind malwarebytes feels there is a difference ( very impressed with the company itself ) – Ramhound Sep 6 '14 at 2:37

If you are installing Avast then Windows Defender won't work. You will see a window saying "This application has turned off and isn't monitoring your computer. If you are using another app to check for malicious or unwanted software, use Action Centre to check that app's status", when you try to open Windows Defender from Control Panel after installing Avast either in Windows 8 or 7.

As we know Avast and AVG are much more capable than Windows Defender, because Windows Defender is not needed when we are using those. I always suggest to use other apps like Avast or AVG than Windows Defender, because Windows Defender mainly scans only for malicious software or apps and still excludes many viruses and other threats.

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  • Who says avg and avast much more capable besides people paid by avg and avast to say that? – Ramhound Sep 6 '14 at 2:25
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    @Ramhound I said it from my experience. I have been using free version of Avast for years and it is very much better than Windows Defender. I don't know about people being paid by Avast or AVG, and I don't want to know that. – Tomin Jacob Sep 6 '14 at 2:31
  • I have had bad experiences with avg wouldn't wish that program on my worst enemy ( the type of person if I had a chance to sucker punch I would). Avg corrupted every single one of my emails when it added a "scan by avg" footer to every single one of my emails(when I still heavily used outlook) – Ramhound Sep 6 '14 at 2:38
  • @Ramhound Did you paid for it ? – Tomin Jacob Sep 6 '14 at 2:41
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    @Ramhound I never tried AVG luckily. I use Avast since early. Before that there was only Windows Defender and it lacks many features like USB scanning and it was very poor in detecting viruses. – Tomin Jacob Sep 6 '14 at 3:09

for me Immunet and Avira works best with windows defender without letting my system slow. Cloud based antivirus solution provides an extra layer of protection to your PC without slowing it down.

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  • You are mentioning Immunet and Avira quite often in your answers, is there an affiliation? – bummi May 8 '15 at 10:59
  • Hi bummy, Sorry for the late response. I am using Avira as a primary and Immunet as a secondary antivirus solution in my system for quite some time now and i am completely satisfied with the service of these two that’s why I recommend these two solutions for other users. – Sophia May 13 '15 at 12:33
  • Hi bummi, extremely sorry for wrong spelling. – Sophia May 14 '15 at 9:35

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