According to the Symantec Security Lab (johnwick.io), hackers launched a denial of service (DoS) attack against the well-known wallet Electrorum server. The hacker used a botnet with more than 140,000 computers to attack Electrum's nodes and deployed malicious nodes at the same time. When a user connects to these malicious nodes and sends a transaction using the old version of Electrum, the user is prompted to update the "client carrying the back door". If the user installs this client as prompted, the private key will be stolen and all digital assets will be lost. According to Electrum official news, millions of dollars in digital currency have been stolen.