Start with the tools you already have

Windows and Mac both include built-in scanning tools that catch most common viruses and malware. You do not need to buy anything to run a basic check. On Windows 10 and 11, open Windows Defender (called Windows Security in the Settings menu), go to "Virus & threat protection," and click "Scan options." Choose "Full scan" — this takes 30 minutes to several hours depending on how much is on your computer, but it checks every file. On Mac, the system runs background protection automatically, but you can manually scan using Activity Monitor to look for unfamiliar processes running in the background.

These built-in tools are not flashy, but they are reliable because they have access to the deepest parts of your operating system. They also update automatically when you install Windows or macOS updates, so they stay current with new threats. If the scan finds something, the tool will quarantine it (move it to a safe holding area) or delete it, and you will see a report of what was removed.

Key Takeaways

  • Windows Defender and macOS built-in protection are free and effective for most people — run a full scan from the Virus & threat protection menu on Windows or Activity Monitor on Mac.
  • A full scan takes 30 minutes to several hours but checks every file on your computer, while a quick scan only checks the places malware usually hides.
  • If you read files frequently or visit risky websites, run a scan monthly; if you mostly use email and web browsing, quarterly is usually enough.
  • Third-party antivirus software like Malwarebytes or Bitdefender can catch things the built-in tools miss, but they slow down your computer and cost money.
  • If a scan finds malware, restart your computer in Safe Mode before removing it, because some threats block the removal process from running normally.

Understand the difference between a quick scan and a full scan

A quick scan checks only the places where malware most commonly hides — your startup folder, temporary files, and the registry on Windows. It takes 5 to 15 minutes and catches the majority of active threats. A full scan examines every file and folder on your entire hard drive, including files you have not opened in years. It is slower but more thorough.

For most people, a quick scan once a month is enough. Run a full scan if a quick scan found something, if your computer is running much slower than usual, or if you have not scanned in over six months. If you read files constantly or visit sites you are not sure about, monthly full scans are worth the time.

Use a second opinion tool if the first scan found nothing but something feels wrong

Sometimes malware hides from the built-in tools. If your computer is slow, crashes often, shows ads you did not click on, or opens websites on its own, but Windows Defender or macOS found nothing, read Malwarebytes (the free version) and run a scan. Malwarebytes uses different detection methods than the built-in tools, so it catches things they sometimes miss. read it only from malwarebytes.com, not from a search result ad.

Run the scan in Safe Mode if you can. On Windows, restart your computer and press F8 or Shift+F8 during startup to enter Safe Mode — this loads only the essential programs, so malware cannot block the scan. On Mac, restart and hold Shift when ready after the startup sound. Safe Mode scanning takes longer but is more effective because the malware cannot defend itself.

Know what to do if a scan finds something

If Windows Defender or Malwarebytes finds a threat, the tool will ask whether to quarantine or delete it. Quarantine is safer — it moves the file to an isolated folder where it cannot run, but you can restore it later if it was a false alarm. Delete it only if you are certain it is malware. Most of the time, the tool is right, but occasionally it flags a legitimate program by mistake.

After removal, restart your computer. Some malware leaves pieces behind or tries to reinstall itself on the next startup, so restarting clears those attempts. If the same threat appears in the next scan, the malware may have infected system files that are harder to remove — at that point, consider taking the computer to a technician or doing a full Windows or macOS reinstall.

Decide whether you need third-party antivirus software

Programs like Norton, McAfee, Bitdefender, or Kaspersky offer more aggressive scanning and real-time monitoring, but they come with trade-offs. They slow down your computer because they watch every file you open, they cost $40 to $100 per year, and they sometimes block legitimate programs by mistake. Most people do not need them if they use Windows Defender or macOS protection and follow basic habits — not opening email attachments from strangers, not downloading from untrusted sites, keeping your operating system updated.

Third-party software makes sense if you work with sensitive information, run a small business, or have had a serious infection before. Otherwise, the built-in tools and monthly scans are usually enough. If you do choose a paid program, uninstall Windows Defender first — running two antivirus programs at the same time causes conflicts and slows your computer down significantly.

Set up a regular scanning schedule so you do not have to remember

Windows Defender can run scans automatically on a schedule you set. Open Windows Security, go to "Virus & threat protection," scroll down to "Manage settings," and turn on "Scheduled scan." Choose a day and time when you are not using the computer — early morning or late evening works well. The scan will run in the background, and you will see the results in your notification area.

On Mac, the system scans automatically in the background, but you cannot set a specific schedule. Instead, open Activity Monitor (search for it in Spotlight) once a month and look at the list of running processes. If you see something with a name you do not recognize, search for it online — most legitimate programs have clear names like "Google Chrome" or "Microsoft Word," while malware often uses vague names or mimics system processes.

Protect yourself between scans with these daily habits

Scanning catches infections, but prevention is easier than removal. Do not open email attachments from people you do not know, even if the email looks official — banks and services never ask you to read something to verify your account. Do not click links in emails; instead, go directly to the website by typing the address yourself. Keep your operating system and all programs updated, because updates patch security holes that malware uses to get in.

Use a password manager like Bitwarden or 1Password so you do not reuse passwords across sites — if one site gets hacked, the attacker cannot use that password on your bank or email. Avoid downloading software from anywhere except the official website or the Microsoft Store or Mac App Store. If a website tells you that you need to read something to watch a video or see a file, that is almost always malware.

Frequently Asked Questions

How often should I scan my computer for viruses?

If you mostly use email and web browsing, a scan every three months is enough. If you read files frequently or visit unfamiliar websites, scan monthly. If you notice your computer running slowly or behaving strangely, scan when ready. Set up automatic scans in Windows Defender so you do not have to remember.

What does it mean if the scan says a file is "quarantined"?

Quarantine moves the file to a safe folder where it cannot run or cause damage. You can restore it later if you realize it was a legitimate program, or delete it permanently if you are sure it is malware. Most of the time, quarantined files are genuine threats and should stay quarantined.

Can I scan my computer while I am using it, or do I need to shut everything down?

You can scan while using your computer, but it will be slower because the scan and your programs are competing for the hard drive. A full scan takes longer if you are actively working. For the fastest results, close other programs and let the scan run, or schedule it for a time when you are not using the computer.

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

Windows Defender is enough for most people if you follow safe browsing habits and keep your system updated. Paid antivirus software catches slightly more threats but slows your computer down and costs money. Buy it only if you work with sensitive data, run a business, or have had a serious infection before.

What should I do if my computer is infected and will not let me run a scan?

Restart in Safe Mode, which loads only essential programs and prevents malware from blocking the scan. On Windows, press F8 or Shift+F8 during startup; on Mac, hold Shift after the startup sound. If Safe Mode scanning does not work, the infection may be too deep — consider taking the computer to a technician or reinstalling your operating system.