The host at this IP address is obviously operated by cybercriminals. It is running a malware botnet controller which is being used to control infected computers (bots) around the globe using a trojan horse.
Malware botnet controller located at 138.91.49.153 on port 51118 TCP:
$ telnet 138.91.49.153 51118
Trying 138.91.49.153…
Connected to 138.91.49.153.
Escape character is ‘^]’
Referencing malware samples:
MD5 46f0c5e1d453127dfa9f7c17f105de48