Disconnect from the internet if you see ransomware notes. Otherwise: update Windows, run a Full scan then a Microsoft Defender Offline scan in Windows Security, uninstall unknown programs, reset your browsers and remove unknown extensions, and change important passwords from a clean device.

Why this happens

Microsoft Defender is built into Windows 10 and 11 and is effective for most infections. The Offline scan restarts the PC and scans before Windows loads, catching malware that hides while Windows runs.

Many “viruses” are actually adware or browser hijackers: unwanted extensions, changed search engines and notification spam. Those are removed in the browser, not by antivirus alone.

Signs of the problem

  • Pop-up ads and browser redirects.
  • Unknown programs or extensions.
  • Security alerts, slow PC, or disabled tools (Task Manager, Defender).

Common causes

  • Bundled software from untrusted downloads.
  • Malicious email attachments or links.
  • Fake updates and cracked software.
  • Allowed browser notifications from scam sites.

Fixes to try, in order

  1. Update and run a full scanWindows Security → Virus & threat protection → Scan options → Full scan.
  2. Run an Offline scanScan options → Microsoft Defender Antivirus (offline scan) → Scan now (PC restarts).
  3. Uninstall unknown programsSettings → Apps → Installed apps; sort by install date and remove suspicious entries.
  4. Clean browsersRemove unknown extensions, reset settings (chrome://settings/reset), and block notifications from unknown sites.
  5. If malware blocks the scansMicrosoft Defender doesn't run in Safe Mode, so use the Offline scan above. If Windows Security won't open at all, run Microsoft Safety Scanner (a free standalone scanner downloaded from Microsoft), or reset Windows with Keep my files.
  6. Secure accountsChange passwords for email, banking and social accounts from a clean device and enable 2FA.
  7. Reset Windows if neededSettings → System → Recovery → Reset this PC, if infections return.
How to confirm the fix: Scans report no threats and pop-ups/redirects have stopped.

Prevent it from coming back

Download software only from official sites, keep Windows updated, and don't allow notifications from unknown sites.