Technology in terms you understand. Sign up for the Confident Computing newsletter for weekly solutions to make your life easier. Click here and get The Ask Leo! Guide to Staying Safe on the Internet — FREE Edition as my thank you for subscribing!

How Do I Run a Full Scan Using Windows Defender?

It’s a common suggestion… do you know how?

A full scan scans things a more common "quick scan" bypasses. Here's how to run one using Windows Security.
Applies to Windows: 10

When people are faced with malware, the hint of malware, the suspicion of malware, or the removal of malware, one of the more common recommendations is to run a full, up-to-date scan with your security software.

I’ll walk you through the process of doing that with Windows Security (aka Windows Defender, aka Microsoft Defender).

Become a Patron of Ask Leo! and go ad-free!


Run a full scan

  • Use Windows Update to make sure Windows Defender is as up to date as possible.
  • In Windows Security, Virus & threat protection, use the “Scan options” to select a full scan.
  • Click on Scan now.

A full scan will take some time and may impact the performance of your system, but you can continue using it if you like.


Before running the scan, you want to make sure your security software is as up to date as possible. With Windows Security, that means running Windows Update.

Visit Updates and Security in Windows settings, and click on Check for updates.

Even if Windows tells you the machine is up to date, click on Check for updates anyway. It’s common for there to be an update for Microsoft Defender.1

Updating Security Information
Updating Security Information. Click for larger image. (Screenshot:

This ensures you have the latest and greatest information and tools available to catch the latest malware.

Windows Security

Click on Windows Security in the left-hand column and then on Open Windows Security in the resulting Settings page.

Windows Security
Windows Security. Click for larger image. (Screenshot:

Click on Virus & threat protection.

Virus & Threat Protection
Virus & Threat Protection. Click for larger image. (Screenshot:

Click on Scan options (the link is just below the “Quick Scan” button).

Full Scan option.
Full Scan option. Click for larger image. (Screenshot:

Click on Full scan and then Scan now to begin the scan.

Full scan underway.
Full scan underway.

As noted in the various messages along the way:

  • A full scan can take a very long time.
  • You can continue to use your computer while it scans, though you may find performance is degraded while the scan continues.

A full scan is no guarantee

I need to point out that running a full scan — even an up-to-date scan with the latest information about the latest threats — is no guarantee that all malware will be discovered and dealt with. This is true for every anti-malware tool. Not all tools catch all malware.

You can never let down your guard.

That being said, though, running up-to-date scans is something you can do to significantly stack the odds in your favor, especially after other forms of malware removal or if you just suspect malicious software on your machine.

Do this

Run a full scan sometime when you don’t need it. You’ll get a sense for what to expect and what it looks like on an uninfected machine.

Don’t be surprised, however, if you do encounter threats, and make sure to quarantine them.

Then next time you have or suspect malware, you’ll have this tool in your arsenal, ready to help you stay safe.

Then, subscribe to Confident Computing! Less frustration and more confidence, solutions, answers, and safety tips in your inbox every week.

Podcast audio


Footnotes & References

1: My theory is it’s updated several times a day as circumstances warrant.

14 comments on “How Do I Run a Full Scan Using Windows Defender?”

    • Yes. Pay no attention to the “Estimated time remaining”. I’ve never seen a time estimate take the time the program says it will.

      Since the scan runs in the background, it shouldn’t matter unless you need to run a resource hungry program.

  1. “A full scan is no guarantee
    I need to point out that running a full scan — even an up-to-date scan with the latest information about the latest threats — is no guarantee that all malware will be discovered and dealt with. This is true for every anti-malware tool. Not all tools catch all malware.”

    You’ve probably read that you should run only one malware program at a time. That means don’t run more than one antimalware program in real-time. It can be helpful to have a second or third antimalware program installed and not running in real time. If you run a scan with your alternate antimalware program(s), it/they might catch something MS Security missed.

  2. Thanks for this. I have been using Norton Anti-virus for many years which does regular scans as well as quick scans. Is there any advantage or disadvantage to also running a Defender scan?

  3. Leo recommended Defender years ago and I have used it with great succes since then. I run a full scan every several months when something in his “Ask Leo! – Confident Computing” reminds me. I did so today on a relatively new Windows 11 HP laptop with SSD and it took 32 minutes. Defender already had stopped and isolated PUABundler:Win32/FusionCore, which I removed. I usually run the Defender Offline Scan at the same time, which took about 5 minutes today–it runs before the OS loads and never has found a problem, for which I credit Defender up front.

  4. I have TRIED to run a scan, any scan in defender. The problem that I have is.. I can’t find where to find “scan”! Is there a big gaping whole in Defender on my box? The dashboard tells me no action needed on all containers. What am I missing? I regularly check. Fire wall is on. Where am I going wrong? Something stupid I’m sure, but I can’t believe it ‘s only me. Well, you know Murphy’s law. Any suggestions?

  5. Re: Windows 11 – A friend of mine downloaded Windows 11 and now finds she cannot open an app caller ‘KARMA’, which is a program to run a karaoke session. It is free if only 3 singers…if more singers you must pay about $150.00. Is there any info you can help solve this problem? …….Les McMillan………


Leave a reply:

Before commenting please:

  • Read the article.
  • Comment on the article.
  • No personal information.
  • No spam.

Comments violating those rules will be removed. Comments that don't add value will be removed, including off-topic or content-free comments, or comments that look even a little bit like spam. All comments containing links and certain keywords will be moderated before publication.

I want comments to be valuable for everyone, including those who come later and take the time to read.