Ransomware is most usually spread through infected attachments in emails. ESET Ireland points out three major issues sticking out from the unfortunate mans story. Free antivirus software is usually not as fully functional as paid security packages, therefore they do not protect against the full range of online threats. External disks, USB sticks, DVDs, online storage like Dropbox or Google drive can all be used for quick and easy backups of all crucial files, documents, pictures, etc. The company has hundreds of people around the world working hard every day so customers computers, tablets, smartphones and servers are properly protected.”]
Source: https://informationsecuritybuzz.com/articles/an-irishmans-experience-with-cryptolocker/