An increasingly common scam by online fraudsters is to smuggle programmes onto a person's computer which encrypt the victim's personal files. In order to regain access to the files, the fraudsters demand that the victim pay money via anonymous payment services.
But you should never do this, advises Germany's Office for Information Security (BSI). Even if you make a payment, there's no guarantee that you'll get access to your files restored.
Instead it's better to have backed up your personal data such as documents and photos regularly on an external hard drive so they can be restored in the case of a scam or a hard drive failure.
Current anti-virus software can often recognise the ransom-ware trojans, but can't prevent the encryption of data. But whoever regularly backs up their files can restore the computer's original state fairly quickly after an attack.