Having same issue starting today on our desktop with Chrome and Windows 10. Was also having it on our laptop with Firefox and Windows 10, but it went away somehow after a Restart and an Avast Virus Scan (which found nothing). After we sent an e-mail from the desktop to the laptop, opening that e-mail caused the laptop to start getting those alerts incessantly. All other e-mails still open normally.
Help, please. Thanks.