Most people think that if they have a pretty good antivirus in place they are safe from any kind of attack from ransomware. Not true.
Even a really good antivirus company like SOPHOS can only protect you from what is KNOWN, they cannot protect you from the unknown until the unknown rears its ugly head and makes itself visible via an attack. Response by a good anti-virus to a new ransomware attack can take 24 – 48 hours, on average. In that amount of time your system can become infected, encrypted and locked away; until you pay the fee.
SO, how do you avoid this scenario? Backups. Without consistent, secure, double redundancy backups you can lose valuable data to ransomware. There are no guarantees out there either; you might pay the fee and STILL not get your information back. Believe me, I have seen this happen more than once. Taking a proactive position when it comes to the protection of your system is always the safest route to travel.