During the twentieth century, the entertainment industry recorded a steady revenue growth. The progress of information and communication technology (ICT) influenced the creation of a new segment in the industry at the beginning of the 80s, known as the video game industry. During the first two decades, the dominant model of earning for video games publishers was sale of a full game, which means that users were obliged to pay in order to play the game (pay-to-play concept). In the past ten years, publishers have developed a new approach, which instead of selling entire game content at once tends to decompose the sale into several smaller transactions. The prices of these supplements are often calculated in the virtual currency that is considered to be the currency of video game, and not in one of convertible currencies, which creates additional confusion. The subject of the paper is to explain the essence of microtransactions as type of electronic payments created in the video games industry and to observe their role in the process of industry transformation.

All current cryptocurrencies are controlled by private entities, so that the issue of impact on monetary system becomes very important. Autonomous decisions by private entities concerning the money supply could diminish the ability of central banks to implement monetary policy effectively. The subject of this paper is the influence of alternative cryptocurrency forms on the monetary system. The aim of this paper is to determine the ability of central banks to conduct monetary policy successfully in conditions of widespread use of cryptocurrencies in payment transactions. The situation in the cryptocurrency market is compared with the phases of Internet development and the current situation on other markets of electronic payment systems. It is concluded that cryptocurrencies do not have the capacity to endanger the traditional monetary system at the current level. Bearing in mind the early maturity of this market, certain predictions of possible future trends have been made. In the case of private cryptocurrency usage growth, central banks could partially or completely lose influence over monetary policy. The proposed solution is the development of national cryptocurrencies that would ensure the retention of seigniorage to central banks and the prevention of further use of private cryptocurrencies in criminal activities.

The objective of the study is to determine whether the Bitcoin forks have produced significant effects on the cryptocurrency market. The event study methodology is used in this paper in order to determine the statistical significance of the abnormal return of leading cryptocurrencies after three Bitcoin forks. The forks were viewed as three isolated events, with the estimations windows and the event windows constructed separately for each of them. There were statistically significant negative effects related to the creation of Bitcoin Gold and Bitcoin SV. Contrary to expectations, there was no statistically important effect throught out the most famous Bitcoin forking and emergence of Bitcoin Cash. Although cryptocurrencies are a current topic, the literature lacks quantitative research dealing with price changes. Without quantitative analysis, it is difficult to conclude whether the return change is a consequence of a statistically significant event The analysis would therefore provide the tool to determine the statistical significance of their impact on the market. A small number of observed cryptocurrencies is the main limitation of this research. Future researches could cover a wider scope of the market and include other famous cases of forking, for example, the Ethereum forks.

The success of various cryptocurrencies' systems has triggered a great interest in their functioning. The fluctuation of their values is very unpredictable, so the periods of growth are often abruptly interrupted by stagnation or a pronounced decline. Nevertheless, a large number of investors have been involved in the processes of mining and trading cryptocurrencies in recent years. When it comes to the negative aspects of cryptocurrencies, the focus is primarily on various forms of cybercrime. The number of hacker attacks using the blackmail software - ransomware, is on the increase. In such cases, cryptocurrencies are often used as a means of paying ransom. However, the energy efficiency of certain types of cryptocurrencies is a less common topic. The Proof-of-Work (PoW) algorithm used for mining in some systems is an energetically intensive and really expensive process, which after economic analysis no longer seems as profitable as it first appeared to be. Cryptocurrency trading could bring a great income to the investors, but also great losses, because it essentially represents a zero-sum game. The sudden increase in the number of miners led to the disturbance on the computer components market, causing the price increase and even the complete disappearance of certain graphics card models. Everything previously mentioned indicates that cryptocurrencies have brought many negative aspects and disturbances. The subject of this paper is the economic aspect of cryptocurrencies based on the PoW algorithm. The aim of the paper is to indicate the economic unsustainability of their current concept, due to the high costs borne directly by participants in the mining process and indirectly by participants in the computer components market.