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Signs your PC may have a virus, and what to check first

Plenty of everyday problems look like a virus but are not. These checks help you tell the difference before you change anything.

Applies to
Windows 11 and 10
Difficulty
Easy
Time
About 8 minutes
Updated

Quick answer

Real warning signs include settings that change by themselves, security tools that switch off, and programs you did not install. Slowness on its own is rarely malware. Check Windows Security first, then run a full scan if anything looks wrong.

Malware is any software designed to harm your PC, steal information or show you unwanted ads. Viruses, spyware, adware and ransomware are all types of malware. The good news: Windows 11 and 10 include Microsoft Defender, which detects and removes most of it.

  1. Look for the real warning signs

    These symptoms are worth taking seriously, especially if several appear together:

    • Your browser's homepage or search engine changed without you doing it.
    • Pop-up ads appear even when your browser is closed.
    • Windows Security or your antivirus has been switched off, and will not stay on.
    • Programs, toolbars or browser extensions appear that you do not remember installing.
    • Friends receive messages or emails from your accounts that you did not send.
    • Files have been renamed with strange extensions and will not open.

  2. Rule out the common false alarms

    These usually have an ordinary cause:

    • A slow PC is far more often caused by startup apps, a full drive or pending updates. See our guide to a slow Windows PC.
    • A website saying "your PC is infected" is almost always a scam page, not a real detection. See fake virus alerts.
    • Notifications from websites appearing in the corner of the screen usually come from a site you once allowed, not from malware.
    • High fan noise after starting up is often Windows Update or Defender doing routine work.

  3. Check the Windows Security dashboard

    Open Start, type Windows Security and open it. Green ticks mean everything is running. Look at Virus & threat protection:

    • If it shows Actions needed, select it and follow the recommendation.
    • If another antivirus such as Norton or McAfee is listed, that product is in charge of scanning. Open it and check that it is up to date.
    • If protection is off and will not turn on, see turn Microsoft Defender back on.

  4. Look for programs you did not install

    Open Settings, then Apps, then Installed apps. Sort the list by Install date and look at anything added recently. Search the name of anything unfamiliar before removing it, because some entries belong to Windows or your PC maker.

    Then check Settings, then Apps, then Startup for unfamiliar entries set to run when you sign in.

  5. Run a quick scan

    In Windows Security, choose Virus & threat protection, then Quick scan. It takes a few minutes. If it finds anything, or if the warning signs in step 1 continue, follow our full guide to removing a virus with Windows Security.

  6. Protect your accounts if something looks wrong

    If friends received messages you did not send, or you see sign-in alerts you do not recognise, change your email password first, from a different device you trust. Then turn on two-step verification for your email, banking and social accounts.

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