A Chicago underpass stain resembling the Virgin Mary has been defaced by graffiti of a devil face.

The stain, under the Kennedy Expressway in Chicago, was tarnished by the demonic purple scrawl sometime within the last two weeks, police told the Chicago Tribune.

The graffiti is a face with horns, a sinister fanged smile and "666."

Catholics first noticed the yellow and white "Virgin Mary" stain in 2005, flocking to the site to leave flowers and candles and to pray.

"We believe it's a miracle," said Elbia Tello, 42, of Chicago, told The Associated Press in 2005. "We have faith, and we can see her face."

It had been vandalized before. Chicago resident Victor Gonzalez was charged in 2005 with scrawling "Big Lie" over the image.

Other graffiti artists added paint to the stain's "eyes" and "mouth" to resemble Edvard Munch's painting "The Scream," the Tribune said.

Worldwide, people have been drawn to images believed to resemble the Virgin Mary seen on windows, fence posts and walls.

Among the best-known in the United States was an image seen in office windows in Clearwater, Fla. Within weeks, a half million people had been to the site.

Glass experts believe the image was created by a chemical reaction and corrosion of the metallic elements in the glass coating, but they could not explain why it took the shape it did. The windows were broken in 2004.

The Illinois Department of Transportation ruled that the Chicago "Virgin Mary" stain was likely the result of salt run-off.

The Associated Press contributed to this report.

Click here to see a photo of the demonic graffiti at the Chicago Tribune.