To secure your SSH connection the password for "root" has to be modified. Please, regularly change this password. Start the Terminal of your Mac or Shell of your Linux computer. For Windows an SSH application such as Putty is necessary.
(Note: For iPhone without installed SSH Server this series of steps is impossible and not necessary) There is a legal issue that hampers the overall SSH usage: Only applications from the Apple "app store" are legal to be used on an iPhone. The SSH solution is often referred to illegal "Jailbreak" solutions which cannot be recommend from legal perspective ;)However, this issue should not be ignored for all iPhones using such SSH solutions.