More about this here: https://www.vlads.me/2017/06/29/writing-a-simple-ssh-bruteforcer-in-go/
This tool is part of the learning process of the Go programming language.
It is not made with malicious thoughts, but it's merely a proof of concept of how easy it is to write a bruteforcer.
Always edit /etc/ssh/sshd_config to disable root login and password authentication. If, by any means, your life depends on having password authentication enabled, make sure to use a strong password.
/etc/ssh/sshd_config:
PasswordAuthentication no
PermitRootLogin no
# Or, if you need to be able to login as root, use publickey-based authentication
#PermitRootLogin without-password
go get -u github.com/vlad-s/gofindssh