there are some unpleasant events related to cryptocurrency, such as the theft of bitcoin in one of the exchangers by hackers, but not the insignificant bitcoin means, errors in the exchanger system is what makes some cases of bitcoin theft and also because of user errors we should be wary of, for example, we always using the same email and password every time we register a bitcoin account, it is a fatal error, we should also change the password every month, it is quite a hassle to do that but it is very important to do. according to my knowledge, the cryptocurrency blockchain system is the best one compared to other cyber security systems.