A botnet targeting the users of the popular Electrum Bitcoin wallet managed to ensnare more than 150,000 hosts at its peak, Malwarebytes security researchers say.
First observed in December 2018, the threat was initially attempting to lure users into downloading a malicious update aimed at stealing their cryptocurrency. By mid-April 2019, threat actors behind the malware anaged to steal around $4 million in Bitcoin from their victims.
In an attempt to keep users safe, the Electrum developers attempted to deliver an update to their users leveraging the very same flaw as the attackers did. They then attempted to exploit a different vulnerability to patch clients, Malwarebytes explains.
Soon after the second attempt, a botnet was observed launching DDoS attacks against Electrum servers, supposedly as retaliation to these patching attempts.
A week ago, the number of infected hosts was just below the 100,000 mark, but it spiked to over 150,000 within a day, Malwarebytes explains. Ever since, it remained seemingly stable at around 100,000 hosts, while the amount of stolen funds has topped $4.6 million.
The security researchers have observed two different distribution campaigns (RIG exploit kit and Smoke Loader) dropping malware known as ElectrumDoSMiner to fuel the botnet, but also identified a new loader also involved in the downloading of this malware.
According to Malwarebytes, however, there are hundreds of malicious binaries that retrieve the threat, meaning that there are likely other infection vectors as well.
Most of the infected bots are located in the Asia Pacific region (APAC), with South America coming in second (Brazil and Peru).
“The number of victims that are part of this botnet is constantly changing. We believe as some machines get cleaned up, new ones are getting infected and joining the others to perform DoS attacks,” Malwarebytes says.