Research paper on Mumblehard
Linux/Mumblehard is a family of malware targeting servers running both the Linux and BSD operating systems. A Mumblehard infected server opens a backdoor for the cybercriminals that allows them full control of the system by running arbitrary code. It also has a general purpose-proxy and a module for sending spam messages.
Mumblehard components are mainly Perl scripts encrypted and packed inside ELF binaries. In some cases, the Perl script contains another ELF executable with the same packer in the fashion of a Russian nesting doll.
Download the paper from here - http://www.welivesecurity.com/wp-content/uploads/2015/04/mumblehard.pdf