The growing of Information and Communication Technologies (ICT) that has been experienced in recent years, has led to new and more sophisticated ways of doing business. Consequently, worldwide organized criminal groups have been able to adapt their activities to new trends in the area of information security. In this paper the problem of cyber-crime as a profitable business and the model Cybercrime-as-a-service (CaaS) are exposed. For this purpose, the ransomware, which is one of the threats that have generated more profit in the last two years, is analyzed. This kind of malware is able to block assets in the victim systems and blackmail their owners with their deletion, if they fail to pay a ransom. In this sense, a game theory model of the behavior of actors involved in a ransomware attack is proposed. The proposed model describes the extortion process between the attacker and victim and estimates the probability of payment of ransom.