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 51.13.32.87 on port 30921 TCP:
$ telnet 51.13.32.87 30921
Trying 51.13.32.87…
Connected to 51.13.32.87.
Escape character is ‘^]’
Referencing malware samples:
MD5 4f40077f28e307d451afb27281494cef