You think there is a virus
How do I know if my computer has a virus and how do I remove it?
Written by The CommonFixes team · fact checked by CommonFixes review desk
Last updated
Short answer
Real infections usually show up as unfamiliar programs, a disabled antivirus, or heavy background activity when you are doing nothing. The quickest thing to try first: disconnect from the internet — Turn off Wi-Fi or unplug the cable. This stops anything sending your information out while you clean up. Most people are done in about 40 minutes.
Full walkthrough below: 5 steps for Windows, rated medium.
Sounds like this
- •Sudden slowness
- •Unknown programs
- •Antivirus switched off by itself
Why it happens
Real infections usually show up as unfamiliar programs, a disabled antivirus, or heavy background activity when you are doing nothing.
Work through these in order
0% done- 1
Disconnect from the internet
Turn off Wi-Fi or unplug the cable. This stops anything sending your information out while you clean up.
- 2
Run a full scan with Windows Security
Open Windows Security, Virus and threat protection, Scan options, and choose Full scan. Let it finish even though it takes a while.
- 3
Run an offline scan
In the same Scan options list choose Microsoft Defender Offline scan. The computer restarts and scans before Windows loads, which catches things a normal scan cannot.
- 4
Add a second opinion
Install Malwarebytes Free and run a scan. Two different scanners catch more than one alone.
- 5
Change your important passwords
Once the machine is clean, change your email and banking passwords from a different device, and switch on two-step verification.
If none of that worked
If threats keep returning after every scan, back up your documents and reinstall Windows using Settings, System, Recovery, Reset this PC. That is the only certain cure.
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Who wrote this and how we checked it
The CommonFixes team
Writer and researcher
We are a small group of people who spend our days repairing laptops and desktops for family, friends and small offices. Every guide here starts with a problem someone actually brought to us, and we only write down the steps that put the machine right.
- Everyday repairs
- Windows and Mac
- Plain language
CommonFixes review desk
Technical editor
Before a guide goes live, a second person walks through it on a real machine and checks each instruction against the maker's own support pages. Anything we cannot confirm is removed rather than guessed at.
- Fact checking
- Safety warnings
- Source links
This guide was last updated on 10 August 2026. If a step no longer matches what you see on screen, tell us on the contact page and we will test it again.
A gentle reminder: back up anything you cannot afford to lose before major repairs. If a step ever feels risky, stop and ask a technician. There is no shame in that.