Plenty of my customers have had the messages but I’ve never figured out where precisely they originated (in terms of what the customer did to get the message to appear), and I’ve never experienced it for myself when browsing on my own PC (though for a very long time I’ve been using either NoScript and/or UBO, these days just the latter). The closest thing I’ve had was when I once mis-spelt the domain name of a mail hosting provider’s webmail system.