Ransomware is a kind of malicious program or a code that tries reach and impact to the personal data of end-users of terminal devices. The ultimate goal are end users and exploiting them in a financial sense through blackmail. The blackmailing software works on the principle of locking terminal devices and encrypting user data stored on the same devices after which they become unavailable to the end user. In the second stage of attack money is drawn from the end users through various channels, very often through cryptocurrency to regain or repurchase their own data. In this paper, blackmail software is described beside other malicious software and the differences between the underlying locking and cryptographic blackmail software are outlined with their basic ways of functioning. The features of some of the current and well known blackmailing software such as WannaCry and Petya have been compared, and a complete comparison is expressed by a table. The facts and the characteristics that are presented, as well as the statistical indicators, create a picture and open the awareness of the main problem, named blackmailing software. For these practical reasons at the end of the work, there are tips and recommendations on how to protect the terminal device and how to change behavioral patterns and bad habits of using these existing terminal devices because security risks drastically fall off with quality prevention and with the end of the blackmail software expansion.