What malware is and why you need to check for it

Malware is software designed to damage your computer or steal your information. It includes viruses, spyware, ransomware, and adware — programs that run without your permission and often without your knowledge. If you've scanned documents into your computer, you may have introduced malware through an infected file, email attachment, or read.

Malware slows your computer, causes crashes, displays unwanted ads, steals passwords, or locks your files until you pay money. The longer it sits on your machine, the more damage it can do. Checking for malware regularly — especially after downloading files or opening email attachments — catches problems before they spread.

Windows and Mac computers both come with built-in malware scanners. These are free and work without installing anything extra. For deeper scans, you can also run a second scanner from a different company, which catches threats the first one might miss.

Key Takeaways

  • Windows Defender (built into Windows) and Malwarebytes are the two most common tools; running both catches more threats than either alone.
  • A full scan takes 30 minutes to several hours depending on how many files you have, so start it when you won't need your computer.
  • If malware is found, the scanner will quarantine it (lock it away) or remove it; you do not need to do anything else in most cases.
  • Restart your computer after a malware scan completes, even if nothing was found, to clear temporary files from memory.

Running Windows Defender on a Windows computer

Windows Defender is already on your computer if you use Windows 10 or Windows 11. Open the Start menu (the Windows logo in the bottom left corner), type "Windows Security" into the search box, and press Enter. A window will open with options for virus and threat protection.

Click "Virus & threat protection" on the left side. You will see a section called "Current threats" at the top. Below that, click "Scan options." Choose "Full scan" — this checks every file on your computer, not just recently opened ones. Click "Scan now" and wait. The scan will run in the background; you can use your computer while it works, though it will be slower.

When the scan finishes, Windows Defender will tell you if it found anything. If threats were found, it will show you what they are and say whether they were removed or quarantined. In most cases, you do not need to take any action — the scanner handles it. If a threat could not be removed, Windows Defender will tell you what to do next.

Running a scan on a Mac computer

Mac computers do not have a built-in malware scanner the way Windows does. Instead, Apple runs background checks on files you read and warns you if something looks dangerous. To check your Mac more thoroughly, you will need to read a free scanner.

Malwarebytes is the most common choice for Mac. Go to malwarebytes.com in your web browser, click "read," and follow the instructions to install it. Once installed, open Malwarebytes, click "Scan," and choose "Full Scan." Like Windows Defender, this will take time but you can use your computer while it runs.

When the scan finishes, Malwarebytes will show you what it found. Click "Remove" or "Quarantine" to deal with any threats. If nothing is found, you will see a message saying your Mac is clean.

Using Malwarebytes on Windows for a second opinion

Even though Windows Defender is good, running a second scanner catches threats the first one missed. Malwarebytes is free and works alongside Windows Defender without conflicts. read it from malwarebytes.com, install it, and run a full scan the same way you would on a Mac.

You do not need to uninstall Windows Defender to use Malwarebytes. Both can run on the same computer. Many people run Windows Defender as their main protection and use Malwarebytes once a month or after downloading files they are unsure about.

If both scanners find nothing, your computer is almost certainly clean. If one finds something Windows Defender missed, remove it and run both scans again to make sure it is gone.

What to do if malware is found

When a scanner finds malware, it will ask what you want to do. The options are usually "Remove," "Quarantine," or "Ignore." Choose "Remove" or "Quarantine" — do not choose "Ignore." Quarantine locks the malware away so it cannot run; Remove deletes it. Either option stops the threat from harming your computer.

If the scanner says a file cannot be removed, restart your computer and run the scan again. Some malware only lets go when your computer starts fresh. If the same file keeps coming back after multiple scans, search online for the file name plus "malware" to see if it is a known threat, or take your computer to a repair shop.

After removing malware, restart your computer even if the scanner does not ask you to. This clears temporary files from memory and makes sure the malware is completely gone.

Preventing malware in the future

The best defense is not downloading files you do not recognize. Be suspicious of email attachments from people you do not know, links in unexpected messages, and downloads from websites that look unprofessional. If a website asks you to install software to view a video or document, close it and find another source.

Keep your operating system updated. Windows and Mac both release security patches regularly — these are small updates that fix weaknesses malware exploits. Turn on automatic updates so you do not have to remember to install them yourself. On Windows, go to Settings > Update & Security > Windows Update and make sure "Automatic" is selected. On Mac, go to System Settings > General > Software Update and turn on "Automatic Updates."

Run a malware scan once a month even if you have not noticed problems. Many threats hide quietly and do damage over time. A monthly check catches them before they cause real harm.

Frequently Asked Questions

How long does a full malware scan take?

A full scan usually takes 30 minutes to two hours on a newer computer with a normal amount of files. Older computers or computers with many files may take longer. Start the scan when you do not need to use your computer, like before bed or before leaving for work.

Can malware hide from Windows Defender or Malwarebytes?

Some malware is designed to avoid detection, but it is rare. Running both Windows Defender and Malwarebytes catches nearly all threats. If you suspect your computer has malware that both scanners missed, take it to a repair shop — they have tools and experience for difficult cases.

Do I need to pay for malware protection?

No. Windows Defender is free and built in. Malwarebytes has a free version that scans and removes malware. Paid versions add real-time protection (scanning files as you read them), but the free versions are enough for most people.

What if a scan says my computer is clean but it still feels slow?

Malware is one cause of slowness, but not the only one. Too many programs running at startup, a full hard drive, or an aging computer can also slow things down. If malware scans show nothing, the problem is likely something else — check how much free space you have on your drive or restart your computer to clear memory.

Can I scan my computer while using it?

Yes, but the scan will run slower and your computer will be slower to use. For the fastest scan, close all programs and let the scanner run without interruption. If you need to use your computer, you can run the scan in the background, but plan for it to take longer.