Scandal rocked both Hollywood and the US tech industry Monday after an apparent massive hack of a cloud data service unleashed a torrent of intimate pictures of celebrities onto the Internet.

Anonymous posters to online message boards boasted of having nude images of scores of female stars including Oscar-winner Jennifer Lawrence and top model Kate Upton.

Early reports suggested hackers had "ripped" private images from tech giant Apple's iCloud online data storage, but the firm made no immediate comment and other services may have been targeted.

Some of the pictures had previously been circulated on message forums, and others appeared fake, but some major stars expressed outrage at a new breach and threatened legal action.

"This is a flagrant violation of privacy. The authorities have been contacted and will prosecute anyone who posts the stolen photos of Jennifer Lawrence," Lawrence's agent told entertainment media.

Upton's lawyer, Lawrence Shore, told Us Magazine: "We intend to pursue anyone disseminating or duplicating these images to the fullest extent possible."

By late Sunday, Twitter had begun suspending accounts that linked to the Lawrence photos, tech news site Mashable reported.

Among the scores of celebrities whose pictures were allegedly stolen were Avril Lavigne, Hayden Panettiere and Hope Solo.

Former Nickelodeon star and singer Victoria Justice said the images claiming to show her nude were anything but the real deal.

"These so called nudes of me are FAKE people. Let me nip this in the bud right now. *pun intended*" she tweeted.

A spokesperson for actress and pop star Ariana Grande told BuzzFeed that images said to be of her are "completely fake."

- 'Creepy effort' -

But horror movie actress Mary Elizabeth Winstead confirmed that some of her private pictures were in circulation and condemned those who stole them and who circulated them.

"To those of you looking at photos I took with my husband years ago in the privacy of our home, hope you feel great about yourselves," she tweeted.

"Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this. Feeling for everyone who got hacked."

The scale of the breach became apparent on Sunday when users of the 4chan message board, a diverse online community that has been criticized in the past for misogyny, began sharing pictures.

AFP