In some cases, it may theoretically violate the Digital Millenium Copyright act in the U.S, and may also fall under relevant corporate espionage statutes in other places.
However, for the most part it is unlikely that any prosecutor will be interested in a case where one private citizen snoops through the phone of another. Perhaps the best answer is "Sometimes it's illegal, but not enough to really matter".
Search warrants.
If they don't have your permission, it is entirely illegal.
Yes, it is generally illegal to search through someone's bag without their permission as it violates their right to privacy and property.
yes, even if the golf course is publicly owned, it is NOT considered a park and you must have permission to be on it. If it is a private course, it is private property and you would be trespassing.
Yes, it is illegal to go through someone's mail without their permission. This is considered a violation of federal law and can result in criminal charges.
It would be illegal for a student to go through the locker of another student without getting prior permission.
Unless s pupil gives another pupil permission to go through their locker, they should not be doing so and it is illegal.
Yes. It's a violation of privacy and creepy unless you have permission from the person whose trash you're digging through.
Downloading books without the author's permission or from unauthorized sources can be illegal and a violation of copyright laws. It is important to obtain books through legal means such as purchasing them or using authorized platforms for downloading.
Watching movies on YouTube can be illegal if the movie is uploaded without permission from the copyright owner. It is important to watch movies through legal and authorized sources to avoid any legal issues.
A student cannot go through the locker of another student without getting permission. This is illegal and they can be charged with theft for taking items that do not belong to them.
Snooping is not a crime, although it is frowned upon. There are exceptions to this though. 1. The file is in a lock box or other file protecting bin 2. The file is classified, or disclosed by the government. 3. You sign a contract stating specifically that you will not view anything other than what you sign for. 4. It is legally protected and, if, or patented with viewing rights reserved. My guess is that you were just asking if snooping on something personal and not in anyway. i.e an online diary. No that is not illegal, but is not recommended if you ever want to get permission to use the computer again.