Madonna in New York. (AP)

New York, Oct. 19 (AP): The hulking security guards standing at the side of a Hunter College lecture hall was a big hint that their usual professor might be taking the afternoon off.

When the lights came up and Madonna walked in, that confirmed it.

The former Material Girl surprised students at a film course who had just seen an advance screening of her tour documentary, I’m Going to Tell You a Secret.

Her appearance was filmed for the MTVU network series Stand In, where celebrities such as Marilyn Manson, Bill Gates, Shimon Peres and Melissa Etheridge have appeared as guest lecturers at colleges. Many of the students were about the age Madonna was when she moved from Michigan to New York, determined to make it first as a dancer, then as a singer.

“I wanted to be different,”she said yesterday. “I wanted to be somebody.”

Asked by a student what drove her to succeed, the 47-year-old pop star said, “It’s one of those things you can’t really answer. You’re either hungry and determined to make it, or you’re not. I know a lot of people who, when they got rejected, they accepted what people said about them. I never did that.”

Madonna, who was raised a Roman Catholic, said she was led toward Jewish mysticism following a spiritual quest that began when she had children.