In a blog post that detailed the characteristics of the malware and the way in which it gained access to a system, Trend Micro said it had been affecting the Asia Pacific region in July.
The major countries affected were Japan, Indonesia, Taiwan, Thailand and India; other countries in the region were only marginally affected.
Fileless malware exists only in the memory of an infected system making detection much more difficult.
Distribution of the new malware infections from July to August 2017.
To enter a system, the EternalBlue vulnerability was used. This exploit was developed by the NSA but leaked on the Web by a group known as Shadow Brokers in April.
Apart from being used in WannaCry, it was also used in a mass ransomware outbreak — known variously as Petya (ransomware that already existed at the time), NotPetya, Nyetya, ExPetr and GoldenEye — that broke out in Europe in June and spread to other regions.
Trend Micro said the new malware was inserted as a backdoor on a Windows system which then installed various WMI scripts. These scripts then connected to the attacker's command and control servers to obtain instructions and download the cryptocurrency miner malware.
The infection flow of the new cryptocurrency miner malware.
The company advised systems admins to restrict and disable WMI as needed to prevent this malware from infecting a system.
"Not all machines require the WMI service. If a machine does not need access to WMI, disable it to eliminate the risk," Trend Micro said. "Microsoft provides a quick guide on how to stop WMI service completely. Microsoft also provides a tool that can trace WMI activity. SMBv1 can also be disabled to reduce the risk to users."
It also pointed out that the entry point for this malware was EternalBlue, for which a patch had been available since March 2017.
"However, there are still a lot of machines exposed to this vulnerability. Ensuring that the operating system, software, and other applications are updated with the latest patches deters threats from using security gaps as their doorways into systems and networks," Trend Micro said.
Graphics: courtesy Trend Micro