However, as there was no confirmation that internal documents were stolen, the incident was not reported to the police nor disclosed to the public, the Asahi Shimbun newspaper reported.
The hacking occurred in April 2020, shortly after the decision was made to postpone the Tokyo Olympics for a year due to the Covid-19 pandemic, which forced many JOC staff members to work from home.
The hacking forced those employees to be cut off from Internet connections, making work from home impossible and temporarily halting operations.
Operations were resumed in about a month after all 60 desktop computers used by the staff were replaced.
An investigation by specialists found ransomware had been used to spread a virus in the JOC computer system.
However, JOC sources said the organization did not receive any specific demand for ransom or a statement from the hackers about the attack.