Windows Security turned off? Turn Microsoft Defender back on

See who is protecting the PC

Open Start, type Windows Security and open it, then choose Virus & threat protection. The top of the page shows the active antivirus.

• Microsoft Defender Antivirus is listed: continue with step 3.
• Another product is listed that you still use: that product is in charge, and Defender being off is normal.
• A product you already removed is listed: continue with step 2.

Remove leftovers of an old antivirus

Windows keeps Defender switched off while it thinks another antivirus is installed. Use the vendor's official removal tool to clear what is left. For Norton and McAfee, see our uninstall guide. Restart afterwards.

Turn on real-time protection

In Virus & threat protection, under Virus & threat protection settings, select Manage settings. Turn on:

• Real-time protection
• Cloud-delivered protection
• Tamper Protection, which stops other programs changing these settings

Update protection definitions

Back in Virus & threat protection, select Protection updates, then Check for updates. Then install any pending updates in Windows Update and restart.

If settings are greyed out or "managed by your organization"

On a work or school PC this is normal; ask your IT team. On a personal PC it can mean leftover software or malware has changed Defender's policies.

• Run a Microsoft Defender Offline scan from Scan options. See how to remove a virus with Windows Security.
• Uninstall unfamiliar programs from Settings, then Apps, then Installed apps.

Optional: periodic scanning alongside another antivirus

If you keep Norton, McAfee or another antivirus, you can still let Defender run occasional extra scans. In Virus & threat protection, open Microsoft Defender Antivirus options and turn on Periodic scanning.