LONDON (AP) — Moscow-based cybersecurity firm Kasperksy Lab is releasing new details about how its software uploaded classified U.S. documents several years ago. The incident is at the center of a controversy over whether the company's popular anti-virus really works as described.

Previous reports alleged that Kaspersky had uploaded National Security Agency files from an intelligence worker's home computer in 2015. Founder Eugene Kaspersky confirmed the incident in a recent interview with The Associated Press, although he said that it occurred in September 2014, that the upload was accidental and that the files were quickly deleted.

A 13-page report published Thursday elaborates on that interview — and carries awkward claims for the NSA worker in question.

Under the heading "An Interesting Twist," Kaspersky says the worker's home computer was compromised by other hackers.