"Hello I'm from Windows" Scam?

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Mum (old) told me she'd had a call from a foreign gent telling her she had a problem with her PC. He got her as far as switching it on and trying to enter some letters and numbers in the "bottom left hand of the screen".

Fortunately she was struggling to understand him and she doesn't think she did it correctly, eventually told him to call back as she needed to speak to me. They called again the following day but again she said she needed to speak to me.

I've now re-iterated to her (for the umpteenth time) she must not speak to any cold callers and must not let people into the house who knock on the door. I've checked the PC and run a scan with MS Security Essentials, should I be looking for anything else ? Does anyone know what they do when they do get into the PC?

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Thanks, is there anything else I should be checking for on the PC? Should I run another Virus/malware checker?

It all looks okay, she hardly switches it on, only really when I'm there, we do a bit of online banking etc.