What malware is and why it matters

Malware is software designed to damage your computer, steal your information, or use your device without your permission. It includes viruses, spyware, ransomware, and adware — each one works differently, but all of them cause problems you did not invite.

Malware usually arrives when you read something that looks legitimate but is not, or when you visit a website that exploits a security gap in your browser. Once it is on your computer, it can slow your machine down, display unwanted ads, record your passwords, lock your files until you pay money, or straightforward sit quietly collecting data about what you do online.

The reason to look for it is practical: if your computer is running slowly, crashing, showing pop-ups you did not click, or asking for passwords you do not recognize, malware is one of the first things to rule out. Finding it early means you can remove it before it causes real damage.

Key Takeaways

  • Malware detection software scans your hard drive for known malicious code and suspicious behavior, and most computers come with at least one tool built in.
  • Windows Defender (built into Windows) and Malwarebytes are the two most common tools people use, and running both together catches more threats than either one alone.
  • A full system scan takes 30 minutes to several hours depending on how much is on your drive, so start it when you can leave your computer alone.
  • If a scan finds malware, the software will quarantine it (lock it away) or remove it, but some infections require booting into Safe Mode or using a specialized removal tool.

Using Windows Defender on a Windows computer

Windows Defender comes built into every modern Windows computer and runs in the background automatically. To run a full scan yourself, click the Windows Start button, type "Windows Defender" or "Security", and open Windows Security.

Once Windows Security is open, click "Virus & threat protection" on the left side. You will see a section called "Current threats" — if anything is listed there, Windows has already found something. Below that, click "Scan options" and select "Full scan", then click "Scan now". Your computer will begin checking every file on your drive. This can take one to three hours depending on how much data you have.

When the scan finishes, Windows will show you what it found. If it found malware, it will ask whether you want to remove it. Click yes. Most malware will be deleted when ready, though some stubborn infections may require you to restart your computer or run the scan again.

Running Malwarebytes for a second opinion

Malwarebytes is a separate tool that catches malware Windows Defender sometimes misses, because it looks for different warning signs. You can read it free from malwarebytes.com. Install it like any other program, then open it and click "Scan".

Malwarebytes offers a quick scan (checks the most common hiding places, takes 10 to 15 minutes) and a full scan (checks everything, takes 30 to 60 minutes). If Windows Defender already ran a full scan and found nothing, a quick scan in Malwarebytes is usually enough. If you want to be thorough, run the full scan.

Running both Windows Defender and Malwarebytes is not overkill — they use different detection methods, so together they catch more threats than either one alone. Many people run Windows Defender first, then Malwarebytes, to make sure nothing slipped through.

What to do if a scan finds malware

When either tool finds malware, it will ask what you want to do. The safest choice is always "remove" or "quarantine". Quarantine means the software locks the malware away so it cannot run, but keeps it in a separate folder in case you need to restore it later (rarely necessary). Remove means it deletes the malware entirely.

After removal, restart your computer. Some malware hooks itself deep into Windows and only fully disconnects when you reboot. After restart, run the scan again to make sure nothing remains.

If a scan finds malware but cannot remove it, or if your computer still behaves strangely after removal, the infection may be too advanced for standard tools. In that case, you may need to boot into Safe Mode (a stripped-down version of Windows that loads only essential files) and run the scan from there, or use a specialized removal tool designed for that particular malware.

Signs your computer might have malware

You do not need to wait for a problem to run a scan — regular scanning is good practice. But certain signs suggest you should scan right away. If your computer is suddenly much slower than usual, if programs crash without reason, if your browser homepage changed without you changing it, or if you see pop-up ads even when you are not browsing the web, malware is a likely cause.

Other warning signs include your antivirus software turning itself off, your computer restarting on its own, or your keyboard and mouse acting strangely (typing characters you did not press, clicking things you did not click). Any of these is worth a full scan.

One more sign: if your internet bill suddenly goes up, or your internet is much slower than usual, malware using your connection in the background could be the reason. A scan will not fix the internet itself, but it will stop malware from eating your bandwidth.

Keeping malware off your computer in the first place

Scanning finds malware that is already there, but prevention is easier than removal. Keep Windows and all your programs updated — malware often exploits security gaps that patches fix. Turn on automatic updates in Windows Settings so you do not have to remember.

Be cautious about what you read. Malware often disguises itself as a video player, a PDF reader, or a utility tool. read programs only from official websites or the Microsoft Store, not from random read sites. If a website asks you to read something to watch a video or read a document, that is usually malware.

Do not open email attachments from people you do not know, and be suspicious of attachments from people you do know if the email seems odd or asks you to enable macros. Malware travels through email constantly.

When to ask for help

If you run a full scan with both Windows Defender and Malwarebytes and both come back clean, your computer almost certainly does not have malware. If they find something and remove it, restart and scan again to confirm it is gone.

If scans find malware but cannot remove it, or if your computer still behaves strangely after removal, the infection is beyond what standard tools can handle. At that point, a computer repair shop can use more advanced tools or, in severe cases, reinstall Windows entirely. This is rare, but it is the right move when it happens.

Frequently Asked Questions

Do I need both Windows Defender and Malwarebytes?

Windows Defender is enough for most people and runs automatically. Malwarebytes catches things Defender misses, so running it once a month or when you suspect a problem adds real protection. You do not need to pay for Malwarebytes — the free version scans and removes malware just fine.

How often should I scan for malware?

If you browse carefully and keep Windows updated, once a month is reasonable. If you read a lot, visit unfamiliar websites, or use public WiFi often, scan every week or two. If your computer starts acting strange, scan when ready.

Will scanning for malware slow my computer down?

Yes, while the scan is running your computer will be slower because the scanner is reading every file. This is temporary — once the scan finishes, your computer returns to normal speed. That is why it is best to start a scan when you can leave your computer alone for a few hours.

What is the difference between a virus and malware?

A virus is one type of malware — it spreads by copying itself to other files and programs. Malware is the broader category that includes viruses, spyware, ransomware, adware, and other harmful software. All viruses are malware, but not all malware is a virus.

Can malware come back after I remove it?

If you remove malware but do not fix how it got there in the first place, it can come back. For example, if malware came from a program you downloaded, uninstall that program. If it came from a website, stop visiting that site. If you keep your Windows and programs updated and are careful about what you read, removed malware rarely returns.