Tech-support scam: fake security alert that locks the browser and asks you to call 'support'

Pages that show a fake Microsoft, Windows Defender or Apple security alert (a blocked or infected computer, an error code, a warning sound), switch the browser to full screen, capture the keyboard and block leaving the page so the visitor cannot close it, and tell the visitor to call a 'support' phone number. The call is the scam: the caller is talked into paying for fake repairs or into installing remote-access software. One campaign places the alert on random subdomains of Azure Storage static websites (*.web.core.windows.net) and passes the phone number in the address (?phone=...), in English ('WIndows Err') and Japanese ('読み込みエラー') versions; its lure addresses are matched even after a site has been taken down. No genuine security warning locks the browser or asks you to phone a number.