Thanks for all the advice - I've been busy locking the stable door and cursing myself for falling for it - it's my curiosity that leads me sometimes to go along with a scam to find out how it works, and spot the hook before it bites.
However, the original reason I posted it here was because it wasn't a random attack - it was targeted at me as a BT customer (I've talked to someone at BT - at least I hope it was BT! - about this).
They already knew when they phoned me on my landline:
my name
my landline number
my address (at least postcode)
my btinternet.com email address - they sent me a very realistic BT email with a 'BT ID PIN' to confirm
my mobile number - a typical 'Hello, BT here' text with the same BT ID PIN
and, clincher, my BT account number (I have a separate note of it and I asked them to recite it for me to confirm)
And in spite of all the warning bells, that's what persuaded me it was BT who were phoning.
My concern for the BT Community is how they acquired this information and whether other BT customers are in danger of receiving similar approaches.
My only cause for optimism is that after I'd eventually had enough ('please log in to online banking to see if there are any suspicious withdrawals'), hung up the phone and turned the laptop off, they tried ringing back several times - I finally let it ring out - which suggests they hadn't actually got everything they expected!
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Although Malwarebytes reports it's clear, I'm still concerned that they might have downloaded something malicious and set boobytraps. And in the longer term, that they've harvested personal information from my hard disk to sell on for identity theft. There's everything from childhood photographs to my Will! Presumably I won't know until I start getting final demands for someone else's debts!
J
