Japan's defence ministry has launched a probe into a possible leak of sensitive data of an under-development 'hypersonic' missile in a large-scale cyber attack on Mitsubishi Electric Corp. Reuters reported on Wednesday that "the ministry suspects hackers stole performance requirements that were sent to several defence industry companies as part of the bidding process for the project". Mitsubishi was one of the companies that received the requirements. However, it did not win the bid to develop a prototype of the weapon. Reuters added the "leaked details may have been range, propulsion and heat resistance". Japan had revealed in 2018 that it was working on hypersonic missiles. Hypersonic missiles are weapons that can fly in the atmosphere at over five times the speed of sound, making them difficult to intercept with most existing air defences. China, Russia and the US are all working on similar hypersonic missiles. In March this year, the Japanese government announced plans to develop two classes of hypersonic weapons: Hypersonic Cruise Missile (HCM) and the Hyper Velocity Gliding Projectile (HVGP). While the hypersonic cruise missile would have a scramjet engine, the latter would "feature a solid-fuel rocket engine that will boost its warhead payload to a high altitude before separation, where it will then glide to its target using its altitude to maintain high velocity until impact", Defense News had then reported. The HVGP would be capable of attacking targets on land and at sea. Defense News reported it would have an "armour-piercing warhead designed specifically for penetrating ‘the deck of the [aircraft] carrier’”. Both weapons are expected to be fielded in the "2024-2028" time frame. The hypersonic weapons are expected to have a range of around 500km. Japan’s hypersonic missiles have been interpreted as being a threat to China's growing fleet of aircraft carriers. China currently has two aircraft carriers in service, with a third under construction.