Among the different types of cyber-attacks ransomware can be considered as one of the most critical attacks. Ransomware is a malicious software that encrypts and capture system files and data until payment of a ransom is delivered by the victim. Recently, there has been a series of cyber-attacks by a well-known offender called WannaCry ransomware, this entity displayed multiple dangerous ransomware intrusions. This paper will discuss on how cybercriminals bypass computer defensive system, and how WannaCry, as well as other types of ransomware, affect overall computer systems. Furthermore, reviews on preventive measures will be considered, that how businesses should counteract against ransomware attacks. This will serve as guidance to control damage in the worst-possible scenarios, i.e., when the computer system has already been infected and data has been held.