I'm sure you have all seen the news relating to the rise in the incidents of Ransomeware. This is where an attacker encrypts all the files on your computer or tablet and demands a ransom to release your files. This can typically be £1000, and even then there is no guarantee that they will do it, they are crooks.
Antivirus software will not protect you, and there is no way to release the encrypted files (even a shop can't do it)
You should do two things to protect yourself.
NEVER open any email or attachment that you do not expect, even if it appears to be from someone you know. If you are unsure, delete it and contact the sender to check that it is genuine.
BACK UP all your important data to somewhere on another system. This could be another PC, an external hard drive or cloud drive. The only solution is to completely format your system and re-install the operating software.
Apart from Ramsomeware there is always a chance that your hard drive could fail without warning any any time.
Think about what you have stored on your PC/laptop/tablet/phone, could you afford to lose it ? If the answer is no, then back it up regularly.