Hi S_S,
Ransomware / Cryptolockers have been a real menace for the past couple years. The articles listed above and in other similar forum threads have much good advice on staying safe and recovering from theses always-changing threats.
It is important to keep defintiions on all endpoints up-to-date (being out of date by a day or two leaves the computer open to sabotage by the most recent variants), use IPS, use a mail security product well, ensure that there is a known good backup of all important material. Most importantly, though, is educating end users not to open suspicious attachments.
Hope this helps! Please do see the other resources shared and add any new questions to this thread, or mark it solved if you have found your answers.
Mick