In comments to the Oxford Union debating society, Assange said the script was a "recent acquisition" but didn't say how it was obtained. A DreamWorks spokeswoman declined to comment on his claim.
Assange was withering about the movie, which is to be released in November, calling it a "mass propaganda attack" on his site's work.
He made the comments to the Oxford Union on Wednesday via videolink from the Ecuadorean Embassy in London, where he has been holed up for more than six months in a bid to avoid extradition.
His speech was posted to the Web late Friday.