Short version: open Windows Security, go to Virus & threat protection, and hit Quick scan. It’s already installed, it’s free, and for most everyday infections it’s genuinely enough. If it doesn’t fully solve things, run a Full scan, then an Offline scan, and if you’re still stuck, bring in Malwarebytes as a second opinion. All of that is explained step by step below.
We see this a lot at the shop. Someone brings in a laptop that’s suddenly “acting weird” — slow, popping up ads it never used to, maybe the homepage changed on its own — and nine times out of ten, the fix starts with exactly what’s below. Nothing fancy, no product to sell you first. Just the same checklist our techs run before anything else.
Signs Your PC Might Have Malware {#signs}
Not everything that’s slow is infected — sometimes it’s just a full hard drive or too many browser tabs. But when a few of these show up together, it’s worth running a scan:
- The computer takes noticeably longer to open programs, and the fan seems to be working overtime even when you’re not doing much.
- Ads pop up outside your browser — that’s usually a giveaway, since legitimate ads don’t do that.
- There’s a toolbar or app installed that you don’t remember putting there.
- Your browser homepage or search engine changed on its own.
- You’re getting more crashes or blue screens than usual.
- Your internet usage spikes even when nothing’s actively running.
- Windows Defender or Windows Update got turned off, and you didn’t do it — this one’s a red flag, because some malware disables protection on purpose.
If two or three of these sound familiar, go ahead and scan.
Scanning with Windows Defender
Windows Defender — Microsoft calls it Windows Security now — comes with every Windows 10 and 11 install. Nothing to download, nothing to pay for. Independent labs like AV-Test have rated it favorably for years, which matters because it means you’re not choosing between “free and risky” versus “paid and safe.” It’s already there, and it’s actually decent.
Quick scan
This checks the spots malware usually hides — running processes, startup entries, that sort of thing. Takes maybe 10 minutes.
- Hit Start, type
Windows Security, open it. - Click Virus & threat protection.
- Click Quick scan.
- Let it run. If it finds anything, Windows will walk you through removing it.
Full scan
Worth doing if the quick scan turned something up, or if the weird behavior is still happening after. This one checks everything on the drive, so depending on how much you’ve got stored, it can take a couple hours — good one to start before bed.
- From Virus & threat protection, go to Scan options.
- Pick Full scan.
- Click Scan now.
Offline scan
Some malware — rootkits especially — are built to hide from scans while Windows is fully running. The offline scan gets around that by restarting your PC into a stripped-down environment first, before the malware has a chance to load and cover its tracks.
- Scan options → Microsoft Defender Offline scan.
- Click Scan now. Your PC restarts, scans outside of Windows (about 15 minutes), then boots back to your desktop with the results.
| Scan type | Time | Use it when |
|---|---|---|
| Quick scan | ~10 min | Routine check, mild symptoms |
| Full scan | 1–4 hrs | Something suspicious turned up |
| Offline scan | ~15 min | Infection won’t go away |
When to Bring In a Second Scanner
Defender’s a solid full-time antivirus. That said, running something else occasionally isn’t a bad habit — different engines flag different things, and dedicated malware removers tend to be quicker at clearing out adware and browser hijackers specifically.
Malwarebytes is what we usually reach for as a second opinion. The free version is scan-on-demand only, not a background antivirus, so it’s meant to complement Defender rather than replace it.
- Grab it from malwarebytes.com directly — steer clear of download mirrors.
- Install it, open it.
- Click Scan.
- Quarantine whatever it flags.
Do you actually need a paid antivirus? Honestly, probably not, if you’re keeping Windows updated and browsing sensibly. Paid suites throw in a VPN, parental controls, identity monitoring — nice extras, but not required just to keep malware off a Windows 10 or 11 machine.
Found Something? Here’s What to Do
- Quarantine or remove it through whichever tool flagged it — don’t just close the window and hope for the best.
- If you think something’s actively sending out your data, disconnect from the internet for a bit (unplug the cable, or turn off Wi-Fi), then reconnect once it’s cleaned up.
- Change your passwords, email and banking first, ideally from a different device — some malware logs what you type.
- Check your browser extensions and delete anything unfamiliar (Settings → Extensions, on Chrome or Edge).
- Run one more full scan after cleanup, just to confirm it’s actually gone.
- Still seeing symptoms after two clean scans in a row? That usually means it’s dug in deeper than a normal scan can reach. At that point it’s worth getting a professional to look, or in stubborn cases, reinstalling Windows outright.
Keeping It From Happening Again
- Leave Windows Update on. Most infections exploit holes that were patched months ago.
- Download software from the source, not from random third-party sites.
- Keep Defender’s real-time protection running, even if you also use another antivirus.
- Windows Firewall should be on by default — worth double-checking it hasn’t been switched off.
- Think twice before opening attachments or links, even from people you know; accounts get compromised too.
- Back up your files somewhere that isn’t permanently plugged into your PC. Helps with malware, and it’s the single best defense against ransomware.
FAQ {#faq}
Is Windows Defender enough on its own? For most people, yes. It’s a real, full antivirus engine, not a stripped-down placeholder — and it’s rated well by independent testers like AV-Test. Adding an occasional Malwarebytes scan gives extra peace of mind, but it’s not a requirement.
Can I scan without installing anything? Yes — Windows Security is already on your PC. Open it from the Start menu and run a scan, no download needed.
How often should I actually scan? Defender’s already scanning in the background all the time. On top of that, a weekly quick scan and a monthly full scan is a reasonable rhythm — plus scan right away anytime something feels off.
How do I know if it’s actually malware and not just a slow PC? Slowness alone isn’t proof. Look for a cluster of symptoms together — pop-ups, a changed homepage, unfamiliar programs, security settings turning themselves off. One of those, probably nothing. Several at once, worth a scan.
Can malware actually dodge a scan? Some can, yes — rootkits especially are built to hide while Windows is running. That’s exactly what the offline scan is for, since it checks your system before the malware gets a chance to load.