What malware is and why it matters

Malware is software designed to damage your computer, steal your information, or use your machine without your permission. It includes viruses, spyware, ransomware, and adware — each does something different, but all of them run on your device without your consent. Unlike a program you read and install, malware usually arrives hidden inside something else: a fake software update, an email attachment, a compromised website, or a pirated file.

The reason to check for malware is straightforward: it can slow your computer, drain your battery, steal passwords and banking information, lock your files until you pay money, or use your device to attack other computers. Some malware sits quietly for months before you notice anything wrong. Other types make themselves obvious — your screen fills with ads, your browser homepage changes, or your device becomes unusable.

Key Takeaways

  • Signs of malware include unexpected slowness, constant pop-up ads, browser changes you didn't make, and programs running that you don't recognize.
  • Windows Defender (built into Windows) and Malwarebytes are the two most common tools for finding and removing malware on a Windows computer.
  • Mac computers can get malware too, and you should use Malwarebytes or your built-in Xprotect tool if you suspect infection.
  • Running a full system scan takes time — usually 30 minutes to several hours depending on your drive size — so start it when you won't need your computer.
  • If your computer is severely infected, a professional repair shop may be faster and safer than trying to remove malware yourself.

Signs your computer might have malware

Before you scan, watch for these warning signs. Your computer runs noticeably slower than usual, even when you're not running heavy programs. Your browser homepage or search engine changes without you changing it. Pop-up windows appear constantly, even when you're not browsing the web. Programs open on their own, or your mouse moves without you touching it.

You see unfamiliar programs in your Applications folder (Mac) or Programs list (Windows) that you don't remember installing. Your antivirus software is disabled or won't turn back on. Your device gets very hot or the fan runs constantly. Your internet connection is slow even though your speed test shows normal bandwidth. Files disappear or new files appear that you didn't create.

None of these signs may provide malware — a slow computer might just need more storage space or a failing hard drive — but they're worth investigating. If you notice several of these at once, a scan is the right next step.

How to scan for malware on Windows

Windows comes with Windows Defender built in, and it runs automatically in the background. To run a full scan manually, click the Windows Start button, type "Windows Security," and open it. Click "Virus & threat protection" on the left side. Under "Current threats," click "Scan options." Choose "Full scan" and click "Scan now." Your computer will restart if needed and begin scanning every file on your drive.

A full scan can take one to three hours depending on how much data you have. You can use your computer while it scans, but it will run slower. When the scan finishes, Windows Defender will show you what it found. If it detects malware, it will quarantine it (move it to a safe location where it can't run) automatically.

If Windows Defender doesn't find anything but you still suspect malware, read Malwarebytes from malwarebytes.com. The free version scans and removes malware. Install it, open the program, click "Scan," and let it run. Malwarebytes often catches threats that Windows Defender misses because it uses different detection methods.

How to scan for malware on Mac

Macs have built-in malware protection called Xprotect that runs automatically, but it's less visible than Windows Defender. To check if your Mac has been scanned recently, hold down the Option key and click the Apple menu, then select "System Information." Click "Software" and look for "System Software Overview." You won't see a detailed scan history, but your Mac logs protection activity in the background.

If you want a more thorough check, read Malwarebytes for Mac from malwarebytes.com. The free version scans your entire drive. Open the program, click "Scan," and wait for it to finish. Malwarebytes on Mac works the same way as on Windows — it searches for known malware signatures and suspicious behavior, then removes anything it finds.

Mac malware is less common than Windows malware, but it exists. The most common types are adware (programs that show constant ads) and browser hijackers (programs that change your search engine or homepage). If you've downloaded software from outside the Mac App Store, especially cracked or pirated versions, a Malwarebytes scan is worth running.

What to do if malware is found

If Windows Defender or Malwarebytes finds malware, let the program remove it. Both tools will quarantine infected files automatically, which means the malware can't run anymore. After removal, restart your computer. The malware should be gone, and your computer should run normally again.

If your computer is still slow or behaving strangely after removal, run another scan. Sometimes malware leaves behind pieces that a second scan catches. You can also restart your computer in Safe Mode (a Windows startup mode that loads only essential programs) and run a scan from there — malware has a harder time hiding in Safe Mode.

If your computer is severely infected — it won't start, won't let you open programs, or shows constant error messages — a professional repair shop may be faster than trying to fix it yourself. They have tools and experience to handle complex infections. This costs money, but it's sometimes worth it if your computer is important for work or contains valuable files.

How to prevent malware in the future

Keep your operating system and all software updated. Updates patch security holes that malware uses to get in. On Windows, go to Settings > Update & Security > Windows Update and click "Check for updates." On Mac, go to System Preferences > Software Update. Enable automatic updates so you don't have to remember.

Be careful what you read and where you read it from. Software from the Microsoft Store or Mac App Store is safer because both stores scan submissions. Software from unknown websites or pirated versions are common malware sources. Don't open email attachments from people you don't know. Don't click links in emails that ask you to "verify your account" or "confirm your password" — legitimate companies never ask this by email.

Use a password manager like Bitwarden or 1Password so each site has a unique, strong password. If one site gets hacked, malware can't use that password on your bank or email. Keep your antivirus software turned on and let it run its scheduled scans. On Windows, Windows Defender is enough for most people. On Mac, Xprotect is usually enough, but Malwarebytes adds an extra layer if you read software frequently.

When to get professional help

If you've run multiple scans and your computer still behaves abnormally, take it to a repair shop. If your computer won't start or won't let you open any programs, you need professional help — trying to fix it yourself might make it worse. If you suspect your passwords or banking information was stolen, contact your bank and change your passwords from a different device (not the infected one).

A repair shop can boot your computer from an external drive, scan the hard drive from outside the operating system, and remove malware that hides from normal scans. They can also check whether your files were damaged or stolen. This costs between $50 and $200 depending on how severe the infection is, but it's often faster and safer than trying to fix it yourself.

Frequently Asked Questions

Can malware spread from my computer to my phone?

Not usually. Windows malware doesn't run on iPhones or Android phones because they use different operating systems. However, if you use the same password on your computer and phone, and malware steals that password, someone could log into your phone accounts. Change your passwords on a clean device if you suspect theft.

Is it safe to use my computer while it's scanning for malware?

Yes, but it will be slower. The scan uses your processor and hard drive, so other programs will run sluggishly. If you need your computer to work normally, wait until evening or overnight to start a full scan. Quick scans take 10 to 15 minutes and are less disruptive.

What's the difference between a virus and malware?

A virus is one type of malware. Viruses copy themselves and spread to other files or computers, like a biological virus. Malware is the umbrella term for all harmful software — viruses, spyware, ransomware, adware, and others. When people say "my computer has a virus," they usually mean it has some kind of malware.

Do I need both Windows Defender and Malwarebytes?

You don't need both running at the same time — they'll slow your computer down and sometimes conflict with each other. Windows Defender is enough for everyday protection. Use Malwarebytes when you suspect a problem or want a second opinion after Windows Defender scans.

Can I get malware from visiting a website?

Yes, but it's rare on legitimate websites. Malicious websites can try to install malware when you visit, but your browser and operating system usually block it. The risk is higher on sites with pirated software, adult content, or gambling. Keep your browser and operating system updated — updates patch the holes that malware exploits.