It happened around 2:30 a.m. Monday when only workers and security guards were supposed to be inside Cobo Center, The Detroit News reported Wednesday.
Attention turned from what's inside to what's on top when a nude woman skipped security and posed on top of the Dodge Challenger on Monday.
Guards found the woman and about a dozen gawkers taking photographs with camera phones, workers told The Detroit News.
"We heard they were all over the Challenger," said Jason Vines, a spokesman for the Chrysler Group, to which Dodge belongs. The company had earlier had tried to give its cars more sex appeal by bringing in fully clothed "Desperate Housewives" star Eva Longoria to pose at its exhibit.
Cobo Director Glenn Blanton said disciplinary action would be taken if employees were involved in the security breach.