My 91 year old dad was called by someone allegedly calling from 'BT' about his computer. By chance, he had been in touch with (the real) BT just a couple of days earlier, so he didn't twig that this might be a scam. They asked for certain numbers to be read out to them, from the computer. My dad can hardly see, so he called my mum in and she started to read the numbers out (this was, of course, to give them access to my dad's PC). Luckily, while all this was going on, my dad suddenly started to get suspicious (he's usually pretty good at not being taken in, despite his advanced years) and told my mum to put the phone down. The advice from his IT expert, who he called immediately, was to turn the computer off, so that they couldn't access it, even if they'd got the number codes. He came round the next day to check it and it was all fine - the scammers hadn't got in but it was a very stressful and worrying experience for both of my parents.