Is it legal to use a keylogger?

I searched around the internet and found this thing:

"I figure anything is fare in love and war. Kinda like that old saying, "if something doesn't feel right then it probably isn't. Myself I took up a strategic location, inconspicuous surveillance then followed up with an iron pipe and a baseball bat."

The dude did this after discovering that his wife is cheating on him... If he knew her better before entering the relationship, he wouldn't be in this position at all. It is one thing to discover that she is cheating on you in the beginning of the relationship and it is completely different thing to catch her after 4 years when you have kids.

After this, there was a discussion on one forum about the question "is it legal to use keyloggers?", there were some interesting points on this topic.

The thing that was decided on the forum was that if you want to stay on the legal side, you shouldn't install a keylogger on any other computer than your own. You have the right to install whatever you want on your computer for whatever reasons. Then you can just wait for the victim to log on Facebook or email and then you can get what you need.

Installing anything on a computer that you don't own without the knowledge of the person that owns the computer might be illegal, especially if you are installing a keylogger which is basically a surveillance tool. So if you want to stay safe, don't do it because you might end up serving jail time.

So the lesson is : "You can do whatever you want on your own computer", however I am not really sure how can someone prove that you are the one that installed the keylogger on their machine, so it might be illegal but hard to prove.

And the internet and this subject in general is basically WILD WEST, there are no clear borders and nobody knows what is allowed and what is not. To many people do this and if all of them went to jail... probably there wouldn't be enough space for everyone...

I think it is something like using torrents, almost everyone does it even if it is illegal... and I am not sure that anyone goes to jail from downloading a torrent.

So, you remember... if you want to be totally safe, install it on your computer. You probably wouldn't have any problems if you install it on another persons computer but it is not totally safe because they might find out and take legal action against you, and if they can prove that you did it... then you might get punished

http://goarticles.com/article/Is-it-legal-to-use-a-keylogger/5096775/