The leaking of hundreds of private and intimate photographs of Hollywood celebrities cast new doubt on the security of popular online storage sites as investigators probed for explanations of the high-profile breach.

Privacy experts joined Hollywood publicists in denouncing the leaks, which flooded websites over the weekend with intimate images of over half a dozen A-list actresses and performers including Oscar winner Jennifer Lawrence, star of The Hunger Games and Silver Linings Playbook.

The breach — regarded as one of the most wide-ranging involving celebrities — has spurred concerns about the security of photographs, videos and documents that millions of Americans store in popular Internet “cloud” accounts. Lawrence’s photographs allegedly were obtained from a personal iCloud account, a service operated by Apple and often used to automatically store photos taken by a user’s mobile phone.

“This is a flagrant violation of privacy,” a spokeswoman for Lawrence said in a statement that threatened to seek prosecution not only of the hacker, but also for anyone who redistributed the photographs. The FBI said that it was looking into the leaks. An Apple spokesman said the company was “actively investigating” apparent breaches of some of its iCloud accounts, but the company did not identify which accounts may have been compromised.