Check Your Windows PC for Malware for Free
Run a free malware scan on your Windows PC using tools you already have — Microsoft Defender and Malwarebytes Free.
3 min read · 5 steps · Checked April 2026
Step 1. Run a full scan with Microsoft Defender
Click the Start button and search for "Windows Security." Click the Windows Security app, then "Virus & threat protection." Click "Quick scan" for a fast check, or click "Scan options" and select "Full scan" for a thorough check of your entire computer. A full scan takes 30 minutes to a few hours depending on your computer's speed and the amount of data on it. Leave your computer running and let it finish.
Step 2. Review what Defender found
When the scan completes, Windows Security shows results. If "No current threats" appears, your computer is clean according to Defender. If threats are listed, click "Start actions" — Defender will automatically quarantine or remove what it found. Quarantine means the file is isolated so it can't do damage. You can review quarantined items under "Protection history" and remove them permanently.
Step 3. Download Malwarebytes Free for a second scan
Open your browser and go to malwarebytes.com. Click "Free Download." Save the installer file, then open it and follow the installation steps. During installation, Malwarebytes may offer a free trial of the premium version. You can accept the trial or decline and use the free version. The free version has full scanning capability.
Step 4. Run a Malwarebytes scan
After installation, open Malwarebytes. Click "Scan" on the main screen. The scan runs automatically, checking for malware, adware, spyware, potentially unwanted programs, and other threats. It usually takes 5 to 20 minutes. When it finishes, it shows a list of any threats found.
Step 5. Remove any threats found
If Malwarebytes found items, they'll be listed with their severity (Malware, PUP, Adware, etc.). Check the boxes next to any items you want to remove — or click "Select All" — then click "Quarantine." Restart your computer when prompted. Malwarebytes places the removed files in quarantine (not permanently deleted) so they can be reviewed before permanent removal if needed.
Quick Tip
Quick Tip — Malware often installs itself when you click a link in a suspicious email, download software from unofficial sources, or click a pop-up saying "Your computer is infected — click here to fix it." Real security software never cold-contacts you this way. Microsoft and Malwarebytes will not pop up in your browser asking you to call a phone number.
If your Windows computer has been running slower than usual, showing pop-ups out of nowhere, sending you to strange websites, or acting up in other ways, malware could be the cause. Malware is a general term for any software installed without your knowledge that does something harmful, from stealing your passwords to sending spam to showing ads you can't close.
The good news: Windows comes with a full antivirus program called Microsoft Defender (once called Windows Defender). It's free, already installed, and updates on its own. For most everyday threats, Defender is enough on its own. You don't need to pay for a separate antivirus if you're running Windows 10 or 11.
For a second opinion, and to catch things Defender might miss, Malwarebytes Free is the most trusted free malware scanner. It's not a replacement for Defender. It's a tool you can run now and then alongside it. The free version lets you scan for malware and remove it by hand. It won't run in the background unless you pay for the premium version.
Run these two scans back-to-back on a regular schedule — perhaps once a month — and you'll catch the vast majority of problems before they cause damage.
Official sources
- Microsoft Support — support.microsoft.com
- Windows Help — support.microsoft.com
- Microsoft 365 Help — support.microsoft.com
Still stuck?
A real person can walk you through it over the phone.
Get help from a person