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 51.104.51.161 on port 2021 TCP:
$ telnet 51.104.51.161 2021
Trying 51.104.51.161…
Connected to 51.104.51.161.
Escape character is ‘^]’
mamapap.giize.com. 120 IN A 51.104.51.161
Referencing malware samples:
MD5 084f90d358f00a94b0402fcbe2cbad52
MD5 7be5351282145411eae97641bdad7763 — AV detection: 50 / 66 (75.76%)