A recent, well-publicized attack on a Japanese business involved two malware families, PlugX and Elirks, that were found during the investigation. PlugX has been used in a number of attacks since first being discovered in 2012, and we have published several articles related to its use, including an analysis of an attack campaign targeting Japanese companies.
Elirks, less widely known than PlugX, is a basic backdoor Trojan, first discovered in 2010, that is primarily used to steal information from compromised systems. We mostly observe attacks using Elirks occurring in East Asia. One of the unique features of the malware is that it retrieves its C2 address by accessing a pre-determined microblog service or SNS. Attackers create accounts on those services and post encoded IP addresses or the domain names of real C2 servers in advance of distributing the backdoor. We have seen multiple Elirks variants using Japanese blog services for the last couple of years. Figure 1 shows embedded URL in an Elirks sample found in early 2016.