If it's an indoor mall, usually that means it's private property. And on private property, it could be a situation where the owners do not allow photography.
What has to be remembered here, is that, that is their rules. It's not law. So, you can break their rules, but ALL they can do is ask you to leave the mall. They CANNOT touch your camera, or delete you're photo's.
Well, it most country's anyway
My policy is to shoot where I like. If a guard comes up and asks me to stop, I do and politely. However, if he/she is rude, I carry on when they are not looking. I always remain polite, even if it comes to a stage where they are escorting me out. The main reason is then they forget about me in a couple of days, and I can always return.
I have heard story's of in the U.S. where police may stop people shooting around government buildings even outside on the street in full public area's. Mainly since Sept 11. That's something entirely different, and I'll leave it up to you guys there to sort that one out.
I was politely asked by a policeman to stop shooting at the central station in Lisbon (below). He was real friendly, and had such a winning smile, well, I just couldn't carry on. Pity as a train pulled in just then and this platform was loaded with people.