Attack overview . Flagpro is used in the initial stage of attacks to investigate target’s environment, download a second stage malware and execute it. Flagpro communicates with a C&amp;C server, and it receives commands to execute from the server, or Flagpro downloads a second stage malware and then executes it. Therefore, Flagpro may have already been used for attacking cases at that point. We call this sample using MFC as “Flagpro v2.0” and old one as “Flagpro v1.0” in this article. Once Flagpro is launched, it communicate with a C&amp;C server and executes the received commands as shown in the above list. If it is not included in both Download Command fields in the command, Flagpro will not execute the main processes such as downloading, executing OS commands, collecting authentication information, and so on. If a Download Command field has “ExecYes”, Flagpro downloads and executes the file. In requesting commands, sending execution results of OS commands or collected authentication information, Flagpro accesses a C&amp;C server with specific URL paths and queries. Following image is an example of the response: Detections . To detect attacks using Flagpro, it is effective to create and install custom signature both on network and endpoint devices. In addition, the investigation commands after Flagpro establishes the connection with the C&amp;C server like following are also useful for detection