That's ridiculous. I understand that some people may have a hangup about the "let it all hang out" type of nursing, but c'mon, the kid was covered with a blanket. That security guard was a jerk.
BTW, our local mall has a very nice little kiosk that has an area for nursing moms, set up by the hospital.
I doubt that a security guard would have taken it upon himself to challenge her, unless she was flaunting it. But since some fool complained, he had to do his job.
If the kid was covered, this implies the act was concealed. Then how did the guard know that she was breast feeding?
The problem comes from the double standard of baring breasts in public places. If you don't have a baby attached to It, it's licentious and lewd. If a baby is attached, it's loving and nurturing. All these women who bare them for a baby would never dream of baring them for show. This logic drives men nuts.