Esther's secret

Esther 2:10 - Esther had not revealed her nationality and family background, because Mordecai had forbidden her to do so.

I wonder why Mordecai refused to let it be known that Esther was a Jew. Hadn't he been the one to enter her in the contest in the first place? Why should he then expect her to keep this a secret? Did no on ask where she was from? If they did ask, I wonder what her answer was. Did she lie? Did she avoid the question? I wonder if she confided in anyone about her nationality and background.