It is so unlikely that anyone would have managed to access your computer, unless you already had a rogue program running, that the caller could not have identified anything – they could even be calling someone who doesn’t have a computer! They are chancers, that’s all.
If they can get past your initial suspicions, you will be asked to run a program or change some settings. This might involve disabling the firewall or allowing a remote connection to their “security department”
All this effort is so that your files and settings can be uploaded, snatched, this might include your Paypal login, online banking credentials, Amazon login, email account etc etc. They will also say there is a fee to fix the problem, anything from £50 to £200 is common. Naturally, they take the money and run .
The solution to this is to tell the scammers to clear off before you do anything you’d regret!
However, assuming you do get taken in, fixing the damage they do can take time and would involve changing all passwords, notifying your bank, cancelling debit/credit cards and then, finally, removing whatever has been installed on the computer and making sure the scammers can’t get back in.
Your local computer engineer would charge you for his/her time and that could set you back another sum – you pay twice!
So, don’t get taken in! This scam has been around for two decades and whilst they can con anyone out of money will be around for alot longer.