The host at this IP address is running a malware botnet controller which is being used to control infected computers (bots) around the globe using a trojan horse.
Loki botnet controller located at 104.21.59.53 on port 80 (using HTTP POST):
hXXp://alenbrooksret.com/mobi/Panel/five/fre.php
$ dig +short alenbrooksret.com
104.21.59.53
Other malicious domain names hosted on this IP address:
caraibasimper.com.br 104.21.59.53
alenbrooksret.com 104.21.59.53