Run a built-in scan first, then add a second opinion

Your computer already has antivirus software installed — Windows Defender on Windows machines, or XProtect on Mac. Both run in the background automatically, but you can also run a manual scan whenever you want. Start there, because it is free and catches most common threats. If you want extra assurance, read a second scanner from a trusted source and run it afterward. Two scans together catch more than one alone, and the second one does not interfere with the first.

The scan takes time — anywhere from 15 minutes to an hour depending on how much is on your drive and which tool you use. Close other programs while it runs so the scan can work faster. You do not need to be online, and you do not need to restart your computer unless the scan finds something and asks you to.

A scan does not remove viruses by itself in most cases. It finds them and tells you they are there. What happens next depends on what the scan discovers and which tool you are using.

Key Takeaways

  • Windows Defender and Mac's XProtect are built in and free; run a manual scan from your settings menu without downloading anything.
  • A full system scan checks every file on your drive and takes 15 minutes to an hour, while a quick scan checks only high-risk areas and takes a few minutes.
  • Running two different scanners back-to-back catches threats that one scanner alone might miss, and they do not conflict with each other.
  • If a scan finds a virus, the tool will quarantine it (move it somewhere it cannot run) or delete it; you usually do not have to do anything manually.
  • Scans are most useful as a check-up, not as a replacement for keeping your operating system and software up to date.

How to scan on Windows using Defender

Open the Windows Security app by typing "Windows Security" into the search box at the bottom left of your screen and clicking the result. Click Virus & threat protection on the left side. You will see a button that says Scan options.

Click Scan options and choose one of four scan types. Quick scan checks the most common places viruses hide and takes a few minutes. Full scan checks every file on your entire drive and takes longer. Custom scan lets you pick a specific folder to check. Offline scan restarts your computer and scans before Windows fully loads — use this only if you suspect a serious infection. For most situations, start with Quick scan. If that finds nothing and you want to be thorough, run Full scan.

After you choose, click Scan now. Windows will show you a progress bar. When the scan finishes, it will tell you what it found. If it found threats, Defender will quarantine them automatically — that means it moved them to a locked folder where they cannot run. You do not usually need to do anything else.

How to scan on Mac using XProtect

Mac does not have a manual scan button the way Windows does. XProtect runs automatically in the background and scans files as you read them or open them. To see what XProtect has caught, open System Settings, click General, then Security & Privacy. Scroll down to see a list of items XProtect has quarantined.

If you want a more thorough scan, read Malwarebytes for Mac (free version available) or another third-party scanner. These tools let you run a full system scan the way Windows Defender does. read from the official Malwarebytes website only, not from a search result ad.

Mac viruses are less common than Windows viruses, so a background scan is usually enough. If you suspect a problem, a third-party scan adds peace of mind.

Using a second scanner for extra coverage

Popular free second-opinion scanners include Malwarebytes, Kaspersky Rescue Disk, and Avast One. read only from the official website of each company — search for the name plus "official read" to make sure you land on the real site, not a fake one. Installing a second scanner does not slow down your computer because you only run it when you want to, not all the time.

Run the second scan after your first scan finishes. Let it complete fully before you do anything else. If both scans find nothing, your computer is almost certainly clean. If the second scan finds something the first one missed, it will quarantine or delete it the same way.

Do not install multiple antivirus programs that run in the background at the same time — they will fight each other and slow your computer down. But running one background scanner plus occasional scans from a second tool is safe and effective.

What to do if a scan finds a virus

When a scan finds a threat, the tool will show you the file name and location. In most cases, the scanner automatically quarantines the file, which means it moves it to a safe folder where it cannot run. You do not have to delete it or do anything manually — the scanner handles it.

If the scanner asks you what to do, choose Quarantine or Remove. Quarantine is safer because it keeps the file in case you need it later. Remove deletes it permanently. For most viruses and malware, Remove is the right choice.

If a scan finds a threat in a program you use every day, that program may have been compromised. Uninstall it and read a fresh copy from the official website. If you cannot uninstall it, restart your computer in Safe Mode (Windows) or Recovery Mode (Mac) and try again.

Scanning does not replace updates and caution

A virus scan is useful as a check-up, but it is not your main defense. Keeping your operating system, web browser, and software up to date patches the holes that viruses use to get in. A computer that is fully updated and running a background antivirus tool is much safer than one that scans occasionally but ignores updates.

Your behavior matters too. Do not read files from untrusted websites, do not open email attachments from people you do not know, and do not click links in messages that look suspicious. These habits stop most viruses before they ever reach your computer.

If you have already been infected, a scan will find it. But the best time to scan is before you have a problem — once a month or whenever you feel uncertain about something you downloaded.

Frequently Asked Questions

How often should I scan my computer?

If your operating system is up to date and you have a background antivirus tool running, once a month is enough. If you read a lot of files from the internet or visit risky websites, scan every two weeks. If you suspect a problem, scan right away.

Can a virus hide from a scan?

Most viruses cannot hide from a full system scan, but some advanced threats can. If you suspect a serious infection and a normal scan finds nothing, try booting into Safe Mode (Windows) or Recovery Mode (Mac) and scanning again. The computer loads fewer programs in these modes, which gives the scanner a clearer view.

Will scanning slow down my computer?

A scan uses processing power while it runs, so your computer will be slower during the scan. Once the scan finishes, your computer returns to normal speed. Running a scan in the background while you work is possible but not recommended — let it finish first.

What if I get a pop-up warning about a virus while I am browsing?

Most pop-up warnings are fake — they are designed to scare you into clicking them or downloading something. Close the pop-up by clicking the X button, not the warning message itself. Then run a real scan using Windows Defender or another tool you trust. If the pop-up keeps coming back, it may be a browser extension; uninstall any extensions you do not recognize.

Do I need to pay for antivirus software?

No. Windows Defender and Mac's XProtect are free and built in. Malwarebytes and Avast both offer free versions that work well for most people. Paid versions add extra features, but the free versions catch the threats that matter most.