Ransom demand
This happens in the following way: a virus that encrypts files gets on the victim's computer, and anyone can become it, from the ordinary user to the employee of a large corporation. Then a fraudster requires a redemption in virtual currency for the decryption of data. So, in June last year, a South Korean web provider paid about $1 million in BTC to cybercriminals.
Fake wallets
Fake wallets for bitcoins, as a rule, have similar names to the reputed wallets and use their logos. They lure customers, in particular, by promising to provide greater anonymity of transactions. There are cases when fake bitcoin-wallets managed to penetrate even Apple and Android application stores disguised as real wallets.
Pyramids
Their creators use the desire of the cryptocurrency owners to increase their capital. To do this, traders are invited to make a deposit and receive high returns, for example, 2-3% per day by attracting new investors. This scheme is an example of a classical pyramid, and, despite the fact that its participants receive the promised profit for a certain period of time, eventually, it collapses.
Scammers from social networks
In this case, fraudsters resort to the old way, namely, they offer users to transfer a certain amount in the cryptocurrency to get back several times more. Trying to implement this scheme, scammers have more than once created in the social networks fake accounts of famous people and published tempting offers on their behalf.
51% Attack
Despite the fact that this has not happened yet, it is possible that having conspired some players can gain control over more than 50% of the computing power of the bitcoin network. As a result, the process of checking payments can fail, and the attackers will have the opportunity to spend the same funds twice.