Not surprisingly, many people will resort to anything to gain access to someone's personal data, when properly motivated. All manner of excuses crop up as to why they are exonerated from any crime or guilt for doing so.
"I know he's cheating" or "I'm only doing it for a prank. I'm not hurting anybody."
Honestly, these are the cheapest, weakest excuses for invading someone's privacy. First of all, if you need to resort to betraying someone's privacy to determine whether you should trust them or not, you should already know by now that you have your answer. If you can't trust your significant other to be faithful, and they can't trust you to keep your nose out of their business, why are you with that person in the first place?
Now that that little slap in the head is over with...let's get on with this the real meat of this article.