How Illegal is This Sort of Thing?

I was not looking for anything of this sort, but the other day I came across something which was called a snapchat spy and after I looked around a bit more I realized that there were many other apps like this. In fact you can find articles on the web which offer the top ten snapchat spying apps and on Gizmodo they have an article asking how the heck this sort of thing is not illegal. I can not believe that, at least if you have this app on a phone that is not your own private property. Obviously I can understand how it could be legal for you to use it on a phone that was your property. If you buy a phone for your girlfriend, your wife or one of your kids, then it would obviously be legal for you to install this sort of app and then use it to spy on the person you allowed to use the phone.

However if you put this sort of thing on a phone that did not belong to you, then it seems like that should at the minimum be an invasion of privacy. It seems to me like it should be a very serious offense. Obviously the main purpose for this sort of thing would be to spy on the other person with the view of finding some sort of prurient content. It is not like you are going to want to do this with no intention of finding some sort of explicit content. It is not something that I could ever imagine doing. I would never stop thinking about what would happen if you were caught. Every woman in the world would think you were some sort of sleazy creep at a minimum. At the most they would think much worse.