Jennifer Lawrence, Kate Upton and Rihanna all affected in attack.
A reported hack on storage service iCloud has resulted in alleged photos of dozens of naked female celebrities being circulated on the internet.
Revealing images purportedly including actress Jennifer Lawrence, model Kate Upton, and singer Rihanna were posted on the forum 4chan before spreading over social media networks such as Twitter.
A spokesman for Jennifer Lawrence said: "This is a flagrant violation of privacy. The authorities have been contacted and will prosecute anyone who posts the stolen photos of Jennifer Lawrence."
While it is unclear whether all of the photos are legitimate, a number of those involved have confirmed the legitimacy of some images.
Actress Mary Winstead tweeted: "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.
"Knowing those photos were deleted long ago, I can only imagine the creepy effort that went into this. Feeling for everyone who got hacked."
Other celebrities, including the actress Victoria Justice, have denied the authenticity of the pictures.
Apple, the owners of iCloud, has been contacted for comment.