There is a looming major problem mainly for small businesses. An email seemingly sent from a reputable financial institution arrives with an attachment. Once you open it a message appears that you are being held to ransom. Your files are encrypted (unreadable) until you pay two bitcoins and instructions for this are given. This costs you about £536. Even after paying this ransom they just leave the files encrypted.
The best thing to do is:- update your virus software; Back up all your files; Disconnect from the internet if it gets through and contact professional help.
I think this advice goes for a lot of unknown attachments.