What began as a surprise holiday greeting at a mall in Niagara Falls is now a YouTube sensation that's already had nearly 25 million hits.

Holiday shoppers grabbing some lunch at Seaway Mall Food Court were treated to the Hallelujah chorus of Handel's Messiah in the flash mob style that has become so popular.

The Christmas chorus took center stage as shoppers enjoyed the unexpected holiday performance.

"To this day, after watching it 20 or 30 times, I still get goose bumps watching and hearing it," said Chris Dabrowski of Alphabet Photography, the Canadian firm that produced the spontaneous serenade featuring 87 members of Chorus Niagara.

The production took seven hidden cameras, eight weeks of planning and more than 100 "tight lips."

"There were more than 175 people who knew this was going to take place on Nov. 13 and everybody kept it a secret. And that is one of the other factors that helped make flash mob a success," Dabrowski said.

Philadelphia's opera company has also given Macy's customers some holiday cheer.

And a high school choir surprised shoppers at a mall in Chattanooga, Tenn. But it's the Niagara Fall's performance that has seen more than 24 million hits and counting on YouTube.