A distributed denial-of-service (DDoS) botnet targeting servers used by the Electrum bitcoin wallet reached 152,000 infected hosts at the end of April.

Malwarebytes began tracking this DDoS botnet and its attacks against Electrum’s infrastructure in the spring of 2019. On April 24, the number of infected machines serving the botnet numbered just below 100,000. The next day, its bot count reached 152,000. This total then fluctuated before settling back down to around 100,000 compromised machines.

According to Malwarebytes’ analysis, the majority of these infected computers are located in the Asia Pacific region. Meanwhile, most of the bots found in the Americas were located in Peru and Brazil.

Earlier in April, Malwarebytes observed attackers using two campaigns to drop ElectrumDoSMiner, the malware that is helping to fuel this botnet. One of those operations involved the RIG exploit kit, while the other used the Smoke Loader malware downloader. Even so, the security firm’s more recent report revealed that threat actors are also now using a previously undocumented loader called Trojan.BeamWinHTTP to help distribute ElectrumDoSMiner.

Putting the Electrum Attacks Into Context

This DDoS botnet is part of an ongoing assault against owners of Electrum bitcoin wallets. As reported by ZDNet, the siege began back in December 2018 when bad actors tricked users into installing a malicious wallet update by exploiting a flaw in Electrum’s software. Attackers then used this fake fix to steal more than 200 bitcoin from affected users in the matter of a week. In total, these actors have stolen the bitcoin equivalent of approximately $4.6 million as of Malwarebytes’ latest report.

In February, Electrum’s developers fought back by exploiting the same flaw to redirect users to install a patched version of the Electrum software. It was this move that likely prompted attackers to retaliate by launching the botnet and targeting Electrum’s servers, as Malwarebytes posited in its mid-April article. These DDoS attacks effectively overwhelmed Electrum’s legitimate nodes so that users had no choice but to connect to the malicious ones.

How to Defend Against a DDoS Botnet

Security professionals can help their organizations defend against a DDoS botnet by creating a secure perimeter around their cloud infrastructure. This perimeter should consist of next-generation firewalls, DDoS traffic scrubbing and anomaly detection. Security teams should also consider enlisting the help of artificial intelligence to improve their organization’s anti-malware defenses and their own effectiveness.