The fastest way to scan your PC for viruses

Windows Defender, built into Windows 10 and Windows 11, can scan your entire PC for viruses without installing anything extra. Open the Windows Security app (search for it in the taskbar), select Virus & threat protection, then click Scan options. Choose Full scan and click Scan now. A full scan takes 30 minutes to several hours depending on how many files you have, but it checks every folder on your drive.

If you want results faster, use Quick scan instead — it checks only the places where viruses most often hide, like your Downloads folder and temporary files. Quick scan takes 5 to 10 minutes and catches most active threats. Run a quick scan first; if nothing shows up, you probably do not have a virus. If something does show up, run a full scan to make sure you caught everything.

Windows Defender runs in the background automatically, so you do not have to think about it. If you see a notification that something was found and removed, that means it worked. You can also check what it has caught by opening Windows Security and looking at Virus & threat protection > Threat history.

Key Takeaways

  • Windows Defender is already on your PC and can scan for viruses without you installing anything — open Windows Security and choose Virus & threat protection.
  • Quick scan takes 5 to 10 minutes and finds most active viruses; full scan takes longer but checks every file on your drive.
  • If Windows Defender finds something, it usually removes it automatically and shows you what it caught in Threat history.
  • Third-party antivirus programs like Malwarebytes or Norton can run alongside Windows Defender if you want a second opinion.
  • Restart your PC in Safe Mode before scanning if a virus is preventing Windows Defender from running normally.

When to use a second antivirus program

Windows Defender is good enough for most people, but if you think you have a serious infection, a second scan with a different program can catch what the first one missed. Malwarebytes is a common choice — it focuses on finding malware that Windows Defender sometimes overlooks. Download it from malwarebytes.com, install it, and run a scan. The free version works fine for a one-time check.

Do not install multiple antivirus programs to run at the same time — they will fight each other and slow your PC down. Instead, run Windows Defender first, then uninstall it temporarily, install Malwarebytes, scan, and uninstall Malwarebytes before turning Windows Defender back on. Or use Malwarebytes' portable version, which does not need to be installed at all.

If you want permanent protection from a different company, you can replace Windows Defender entirely. Programs like Norton, McAfee, and Bitdefender all work, but they cost money and run in the background constantly. For most people, Windows Defender is enough — add a second scan only if you think something got through.

Scanning in Safe Mode when your PC will not start normally

If your PC is running very slowly, crashing, or showing strange pop-ups, a virus might be blocking Windows Defender from working. Restart your PC in Safe Mode, which loads only the bare minimum of programs and drivers. In Safe Mode, Windows Defender can often find and remove infections that it cannot touch while everything else is running.

To enter Safe Mode on Windows 10 or 11, restart your PC and hold down the Shift key while it boots. You will see a menu — select Troubleshoot, then Advanced options, then Startup Settings, then Restart. When the PC boots again, press 4 or F4 to choose Safe Mode. Your screen will look different and some programs will not work, but that is normal.

Once in Safe Mode, open Windows Security and run a full scan. This scan will take longer than usual because Safe Mode is slower, but it has a better chance of finding stubborn infections. After the scan finishes and removes anything it finds, restart your PC normally. If your PC runs better afterward, the scan worked.

What to do if a scan finds a virus

When Windows Defender or another antivirus finds a virus, it usually removes it automatically and puts it in quarantine — a locked folder where it cannot run. You will see a notification saying something like "Threat found and removed." That is the normal outcome, and you do not have to do anything else.

Check Threat history in Windows Security to see what was found. Most of the time, the list shows files that were already removed. If you see something you recognize — like a program you installed on purpose — you may have downloaded it from an unsafe source. Uninstall that program and do not download from that website again.

If a scan finds dozens of threats or your PC is still behaving strangely after removal, the infection may be deeper than a single scan can handle. Restart in Safe Mode and run another full scan. If the problem continues, consider backing up your important files and reinstalling Windows — that is the most reliable way to remove a serious infection, though it erases everything on your PC.

Signs your PC might have a virus

A virus does not always announce itself. Watch for these signs: your PC runs much slower than usual, programs crash or freeze, your internet is slower even though your connection is fine, you see pop-ups you did not click on, or your antivirus program is disabled and you cannot turn it back on. Any of these can mean a virus is running.

Strange behavior does not always mean a virus — a full hard drive, too many browser extensions, or outdated drivers can cause the same symptoms. But if your PC suddenly changed and you did not install anything new, a scan is worth running. It takes 10 minutes for a quick scan and costs nothing.

If your PC will not start at all, or Windows Defender will not open no matter what you try, the infection is serious enough that Safe Mode scanning may not work. At that point, you may need to use a bootable antivirus tool — a program you run from a USB drive before Windows even loads. Kaspersky Rescue Disk and Bitdefender Rescue Environment are two examples, though using them requires some technical knowledge.

Keeping your PC from getting infected in the first place

The best virus protection is not getting infected at all. Keep Windows updated — go to Settings > Update & Security > Windows Update and click Check for updates. Windows patches security holes regularly, and viruses often use old holes to get in. Restart your PC when Windows asks you to.

Do not download programs from random websites. Use the Microsoft Store, the official website of the program you want, or a trusted source like GitHub. Avoid clicking links in emails or messages from people you do not know. If a website asks you to download something to watch a video or see a picture, close the tab — that is how many viruses spread.

Be careful with USB drives and external hard drives from other people. Before opening files on them, scan them with Windows Defender. Turn on Real-time protection in Windows Security — it runs in the background and stops viruses before they can do damage. You can check that it is on by opening Windows Security and looking at Virus & threat protection > Manage settings.

Frequently Asked Questions

How often should I scan my PC for viruses?

If Real-time protection is on in Windows Security, you do not need to scan manually very often — Windows Defender is watching all the time. Run a quick scan once a month if you want peace of mind, or whenever your PC starts acting strange. If you download a lot of files from the internet, scan weekly.

Is Windows Defender enough, or do I need to buy antivirus software?

Windows Defender is enough for most people. It catches the majority of viruses and malware, and it is free. You only need to buy something like Norton or McAfee if you want extra features like a VPN or password manager, or if you work with sensitive data and want the strongest possible protection.

What does quarantine mean?

Quarantine is a locked folder where Windows Defender puts files it thinks are dangerous. The files cannot run or spread from there. You can see quarantined files in Windows Security under Virus & threat protection > Threat history. You can delete them or restore them if you change your mind, but most of the time you should just leave them there.

Can I scan my PC while I am using it, or do I have to stop everything?

You can scan while you work, but your PC will be slower. Quick scan does not slow things down much, but a full scan will make everything lag. Run a full scan when you are not using your PC — overnight or while you are away — so the scan can finish faster and you do not have to wait.

What if Windows Defender says a file is a virus but I know it is safe?

Sometimes antivirus programs flag legitimate files by mistake, especially new programs or files from small developers. If you are sure a file is safe, you can restore it from quarantine. Right-click the file in Threat history and choose Restore. But if you are not sure, leave it quarantined — it is safer to be cautious.