When I attended Business College for Travel/Tourism/Airlines...one of my professors showed us all the different ways of getting access to the contents of locked luggage. He told us there is NO LOCK that will prevent anyone from getting into a person's luggage. He demonstrated several techniques and it did not surprise me. The easiest are those nylon type baggage with plastic zippers. I found one of the "tricks" he showed us, demonstrated on YouTube and wanted to share it with you so you would be aware of it on your next trip. It's very informative, yet at the same time TOO informative for thieves who will see this.
You can also find other "tips" and "Tricks" on luggage security on YouTube by doing a "Luggage Security" search on that site.