False virus warning in the browser

Stay calm during alarm windows and calls

Read the complete step before making changes. Stop if unsure or if new warnings appear.

Don't click anything and don't call anyone
A website that shows a phone number and claims your PC is locked may be a scam. Do not call the number displayed, do not pay anything and do not install any remote maintenance software when requested.
Close browser
Try Alt + F4. If the window blocks: Ctrl + Shift + Esc → Highlight browser → End task. Unsaved forms will be lost. Then do not open the suspicious tabs again.
Check with Windows Security
Open Start → Windows Security → Virus & Threat Protection → Scan Options → Full Scan. Use a reputable virus protection that you already have, not the download from the warning message.
Act immediately if access is granted
If anyone had remote access: disconnect from the internet and get trusted professional help. Change affected passwords from another, secure device. If you make payments or disclose bank details, immediately inform your bank via their known contact channels.