How to Check If Your Computer Has Malware

Signs your computer might have malware

Malware is software designed to damage your computer, steal your information, or use your machine without your permission. The most common signs are a computer that runs slowly, programs that crash or freeze, a browser that redirects to unfamiliar websites, or pop-up windows that appear even when you are not browsing. You might also notice your antivirus software is disabled, your files have disappeared, or your internet bill has jumped because something is using your bandwidth.

Not every slow computer has malware — a full hard drive, too many browser tabs, or old hardware can cause the same symptoms. But if your computer was fast last month and is sluggish now, or if you see unfamiliar programs in your installed software list, malware is worth investigating. The sooner you check, the sooner you can stop it from spreading or stealing data.

Key Takeaways

Windows Defender (built into Windows) and Malwarebytes are the two most common tools for scanning and removing malware on personal computers.
A full system scan takes 30 minutes to several hours depending on your hard drive size, so run it when you do not need your computer.
Restart your computer in Safe Mode before scanning if malware is actively running, because Safe Mode loads only essential programs and gives your antivirus a better chance to remove threats.
If a scan finds malware, let the tool quarantine or remove it — do not try to delete files manually, because you might accidentally remove something your computer needs.
After removing malware, change your passwords for email, banking, and other sensitive accounts from a different device if possible.

How to run a malware scan on Windows

Windows 10 and Windows 11 come with Windows Defender, an antivirus program that is already installed and runs in the background. To run a full scan, open the Start menu, type "Windows Security" and press Enter. Click "Virus & threat protection" on the left side, then click "Scan options" and select "Full scan." Click "Scan now" and Windows Defender will begin checking every file on your computer.

A full scan can take one to four hours depending on how much data you have. You can use your computer while it runs, but it will be slower. If you want a faster check, choose "Quick scan" instead — this takes 10 to 15 minutes and checks only the places where malware most often hides, like your startup folder and temporary files. A quick scan catches most common threats, but a full scan is more thorough if you suspect a serious infection.

If Windows Defender is disabled or you want a second opinion, download Malwarebytes from malwarebytes.com. The free version scans and removes malware. Install it, open the program, and click "Scan" on the left side. Choose "Threat Scan" for a faster check or "Full Scan" for a complete inspection. Malwarebytes often finds threats that Windows Defender misses, so running both tools gives you better coverage.

How to run a malware scan on Mac

Macs are less commonly targeted by malware than Windows computers, but infections do happen. macOS comes with XProtect, a built-in antivirus that scans files automatically when you download them. You cannot run a manual scan with XProtect, but you can download Malwarebytes for Mac from malwarebytes.com, which works the same way as the Windows version.

Open Malwarebytes, click the "Scan" button, and let it run. If you suspect a serious infection, restart your Mac in Safe Mode first: shut down your Mac, turn it back on, and hold the Shift key until you see the login screen. Safe Mode loads only essential programs and makes it easier for Malwarebytes to remove threats. After the scan finishes, restart normally.

What to do if malware is found

When a scan finds malware, the tool will ask whether you want to quarantine or remove it. Quarantine moves the infected file to an isolated folder where it cannot run or spread. Removal deletes the file entirely. For most threats, quarantine is safer because if the tool makes a mistake, you can restore the file later. Let the tool handle the removal — do not try to manually delete files, because you might accidentally remove something your computer needs to run.

After the scan completes and malware is removed, restart your computer. Then open your web browser and check that your homepage and search engine are back to normal. If they are still redirecting to unfamiliar sites, the malware may not be fully gone. Run another scan, or consider taking your computer to a repair shop if the problem persists.

Restarting in Safe Mode for a deeper clean

If malware is actively running and preventing your antivirus from working, restart your computer in Safe Mode before scanning. Safe Mode loads only the bare minimum programs your computer needs, which stops malware from running and gives your antivirus a clear path to remove it.

On Windows 10 or 11, restart your computer and repeatedly press the F8 key before the Windows logo appears. (On some computers, it is Delete, Esc, or another key — your computer's startup screen will tell you which one.) Select "Safe Mode" from the menu. On Mac, restart and hold Shift until you see the login screen. Once in Safe Mode, open Windows Defender or Malwarebytes and run a full scan. When the scan finishes, restart normally.

Protecting your accounts after malware removal

Malware often steals passwords and personal information before you catch it. After you remove malware, change your passwords for email, banking, shopping sites, and any other accounts with sensitive data. If possible, change these passwords from a different device — a phone or tablet — so that if malware is still hiding on your computer, it cannot capture your new passwords as you type them.

Start with your email password, because email is the master key to resetting passwords on other sites. Then change your banking and financial account passwords. If you used the same password on multiple sites, change those too. Consider using a password manager like Bitwarden or 1Password to create and store unique passwords for each site, which makes it much harder for stolen passwords to compromise multiple accounts.

Preventing malware in the future

The best defense against malware is not downloading it in the first place. Do not open email attachments from people you do not know, do not click links in unexpected messages, and do not download software from unfamiliar websites. Stick to official sources: the Microsoft Store for Windows programs, the App Store for Mac, and the official websites of companies whose software you trust.

Keep your operating system and browser updated. Windows and macOS release security patches regularly, and installing them closes the holes that malware uses to get in. Turn on automatic updates so you do not have to remember. Run Windows Defender or your antivirus in the background at all times — it will scan files as you download them and catch most threats before they can run.

Frequently Asked Questions

Can malware hide from antivirus scans?

Some advanced malware can hide from basic scans, which is why running a full scan instead of a quick scan matters. Restarting in Safe Mode also helps, because it stops malware from running and protecting itself. If a scan finds nothing but your computer still behaves strangely, try a different antivirus tool — Malwarebytes sometimes finds threats that Windows Defender misses, and vice versa.

Is the free version of Malwarebytes enough?

Yes. The free version scans and removes malware just as well as the paid version. The paid version adds real-time protection that watches your computer constantly, but Windows Defender already does that. Use the free version to scan when you suspect a problem, and rely on Windows Defender for ongoing protection.

What if my antivirus is disabled and I cannot turn it back on?

Malware sometimes disables antivirus to avoid being detected. Restart your computer in Safe Mode, which stops malware from running. Then open Windows Defender or Malwarebytes and run a scan. Once malware is removed, your antivirus should turn back on automatically when you restart normally.

Do I need to scan my phone for malware?

Phones are less vulnerable to malware than computers, but it can happen. On iPhone, malware is extremely rare because Apple controls what software can be installed. On Android, download apps only from the Google Play Store, keep your phone updated, and consider running a scan with Malwarebytes for Android if you suspect a problem.

How often should I scan for malware?

If your antivirus is running in the background and you are careful about what you download, a monthly full scan is usually enough. If you frequently download files from the internet or visit unfamiliar websites, scan every two weeks. If you suspect an infection, scan immediately and then again a few days later to make sure it is gone.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.