Penthouse's notorious film, "Caligula," got into the wrong hands and is now being illegally hawked online ... according to a new suit.
Penthouse claims a New Jersey man, Jeremy Frommer, bought the contents of a storage locker at auction back in 2012 that contained the works of magazine founder Bob Guccione ... including items "Caligula" related.
According to docs ... Frommer formed a company called Guccione Collection with the intent of selling Bob's stuff -- including digital copies of the flick.
Problem is ... Penthouse claims it acquired all rights to the film in 2016, yet Frommer was hawking it on Vimeo as recently as May.
Penthouse wants Frommer to stop selling anything associated with "Caligula" ... and it wants any profits he made.
Jeremy's company issued a statement Friday, saying it "believes the lawsuit is without merit and intends to vigorously defend against it."