A sudden, alarming pop-up claiming your computer is infected with a virus, often with a loud warning sound and a phone number to call "immediately", is one of the most common ways fraudsters gain remote access to victims' computers.
A malicious website or ad triggers a full-screen pop-up mimicking a genuine security warning, often locking the browser to prevent easy closing and displaying a phone number for "Microsoft" or "Apple support". Calling connects you to a scammer who talks you through installing remote access software, then either charges for fake "repairs" or uses the access to steal data directly.
Do not call the number. Close the browser entirely — using Task Manager (Ctrl+Alt+Delete on Windows) if it won't close normally — rather than clicking anything within the pop-up itself.
Restart your device and run a genuine antivirus scan if you're concerned.
Never install remote access software at the request of an unsolicited caller or pop-up, regardless of who they claim to represent.
If you've already granted remote access, disconnect from the internet immediately, run a full antivirus scan, and change your passwords from a different, uncompromised device. Report it to Report Fraud at reportfraud.police.uk.
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If you shared any personal or payment details during a fake support call, check whether your data has appeared in a breach.
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