Researchers Jérôme Segura, Adam Thomas and S!Ri said in a blog post the amount of cryptocurrency stolen was about US$4.6 million in value.
The botnet was flooding the Electrum infrastructure and the number of machines had grown to 152,000 at its peak. Only Windows machines had been observed to be part of the botnet, Segura told iTWire.
New Trojan.BeamWinHTTP connected to ElectrumDoSMiner.
The researchers said they had been able to tie two distribution campaigns — RIG exploit kit and Smoke Loader — that were adding to the botnet by dropping malware which they had detected as ElectrumDoSMiner.
"Now, we have just identified a previously undocumented loader we call Trojan.BeamWinHTTP that is also involved in downloading ElectrumDoSMiner (transactionservices.exe)," they said.
Segura, Thomas and S!Ri posted graphs from VirusTotal showing the hundreds of malicious binaries that were retrieving the ElectrumDosMiner.
The main infrastructure hosting ElectrumDoSMiner binaries and configuration files.
An analysis of the IP addresses that were infected showed that most were from the Asia-Pacific region. The Americas, most bots were in Brazil.
In an earlier post about the same issue, the researchers said that threat actors had tricked users into downloading a malicious version of the wallet.
Presumably, this was version 3.3.3 which was vulnerable to a phishing attack. The Electrum developers have released 3.3.4 to fix this issue.
Asked whether Electrum was aware of the issues, Segura told iTWire: "Electrum is aware of those issues as you can see through their tweets about these incidents."
He said the malicious updates had been effected by using a vulnerability with the Electrum software. "The Botnet attacking the Electrum infrastructure could be in response to Electrum fixing the vulnerabilities and taking down the phishing sites," he added.
Asked why the Electrum issues were not being reported to German authorities, Segura said users had definitely been reporting the DDoS and thefts.
As Electrum has versions for Windows, OSX and Linux, iTWire asked whether all the binaries were vulnerable to being drafted into the botnet. "We've only identified Windows machines in the botnet (while the malicious Electrum wallets do, as you say, affect all operating systems)," Segura replied.
Graphics: courtesy Malwarebytes