VERY IMPORTANT

Bots can use various methods to establish a line of communication between themselves and their command-and-control (C&C) server. Usually, these are done via HTTP or other TCP/IP connections. However, we recently encountered a botnet that uses a more unusual method: an FTP server that, in effect, acts as a C&C server. Using an FTP server has some advantages. It is less common, and this fact may allow it to slip unnoticed by administrators and researchers. However, this also leaves the C&C traffic open for monitoring by others, including security researchers. In addition, thanks to a coding mistake by the attackers, this particular backdoor does not always run the right commands.