Abstract-- Malware or malicious software are exist everywhere, internet or locally. This paper present a category of malware which cybercriminals (hackers, crackers, etc.) currently using for monetizing around the world via internet. Ransomware is the name of this category of malware and it has a variety of families inside it. There are two famous basic types crypto ransomware and locker ransomware. Crypto ransomware usually encrypt personal files of the victims with different cryptography algorithms according how crypto ransomware is designed. These cryptographic alogorithm might be symmetric (single key) or asymmetric (double key, public key). The second type of ransomware lock the victim device (personal computer, mobile device, etc) and prevent the user from accessing it. The countermeasures how to keep secure and safe our systems or network against this dangerous type of malware will be discuss also.