Ransomware such as Cryptolocker is the name given to a type of malware that locks your files and holds them for ransom, requiring you to pay a fee to unlock them.
Business owners who fall victim to ransomware are faced with a hard choice: Pay the $500 ransom or lose potentially priceless data. The choice is, unfortunately, often to pay the ransom. This is unfortunate because it literally funds the next wave of ransomware attacks, and it is for this reason that these attacks are becoming increasingly sophisticated and common.
The most common infection vector is what is commonly known as Phishing, or tricking users to click on something to install the file. User education combined with in-network malware/phishing scanning is the most effective way to prevent a ransomware infection. Remind your users that you will never ask them for their password and to immediately report any suspicious activity to IT.