When I use a 'new device' to get into a Santander account. I' get a message saying that 'we do not recognise this computer' and they send me a text message with a code to input.
How Santander do this I know not, but assume that they look at the mac address. I'm wondering if BT are doing this with his email account, and that something is stopping him seeing a pop-up message on the laptop?