The group, Nullbulge, said it had gained access to thousands of communications from Disney employees and had downloaded “every file possible”.
It is not clear how commercially sensitive the information is for the media and theme park giant, but it is reported to include messages about upcoming projects the firm is working on.
“Disney is investigating this matter,” a company spokesperson told the BBC in an email.
Nullbulge’s website says the group targets anyone it believes is harming the creative industry by using content generated by artificial intelligence (AI), which it describes as “theft”.
The BBC has made contact with the hackers who claim to be in Russia and say they got into Disney’s internal Slack messaging system through an insider.
But when asked for a sample of the stolen data to verify its authenticity, the hackers did not respond – meaning the BBC has not been able to independently assess if the huge data trove is genuine.
“Disney was our target due to how it handles artist contracts, its approach to AI, and its pretty blatant disregard for the consumer,” the hackers claimed.
They said they released the data because they didn’t expect Disney to meet their demands to stop using AI.
It is unusual for hackers to claim they are “Russian hacktivists” with an ethical agenda – most cyber criminals, including those in Russia, aim to make money by extorting their victims.
The leak was first reported in the gaming press and then picked up by the Wall Street Journal, which said some of the leaked material related to advertising campaigns and interview candidates, with some dating back as far as 2019.
There has been growing concern amongst performers, artists and other creatives that the rapid spread of generative AI will undermine their livelihoods and damage the creative environment.
Generative AI is trained on vast bodies of existing material – including texts, images, music and video.
It is then able to produce new work of a standard that can be hard to distinguish from human-generated material.
Some artists and authors have claimed AI firms breached copyright by using their original work to train these AI tools.
Nullbulge describes itself as “a hacktivist group protecting artists’ rights and ensuring fair compensation for their work”.
“Our hacks are not those of malice, but to punish those caught stealing,” it says on its website.
“We will work tirelessly to develop and implement solutions that protect the rights and livelihoods of artists in the digital age.”
The Walt Disney company’s businesses range from film-making and streaming services Disney+ and Hulu, to video games and theme parks dotted across the globe.
It owns the hugely successful Marvel and Star Wars franchises.
