ACC plunged into a far-reaching scandal after Ms Pullar went to the media with the file this year.
Yesterday, ACC's privacy officer, Miriama Henderson, responded to the ACCforum post. "If you've received information not about you, ACC needs to recover the information so we can contact the clients whose information has been released. We'll also advise the Office of the Privacy Commissioner of any breach," she wrote.
Last night, an ACC spokeswoman confirmed the corporation was investigating the potential breach, but had been unable to identify the claimant.
Since the Pullar affair came to light in March, ACC has been hit by a string of further privacy breaches.
Last month, the Herald reported that a former Auckland builder was sent a document about a Te Atatu brain injury victim among papers about his own case.