The United States reportedly has alleged that the designs of Lockheed Martin's F-35 were stolen by Chinese hackers to build the fifth-Gen Chinese Stealth Fighter - FC-31 Gyrfalcon, which commonly goes by the name of J-31.

According to a report published in Economic Times, US defence and strategic affairs experts have accused China of stealing the designs and implementing it on its so-called indigenously developed fifth generation fighter jet.

The American experts also have said Chinese hackers stole the designs in April 2009 from the servers of Lockheed Martin.

Since 2012, when the Chinese J-31 fighter made its maiden flight, aviation experts have commented on similarities that it shared with the F-35. A report in the Aviation Week had noted that even "the J-31's wingspan is an F-35-like 37.5 feet."

Besides that there are several other similarities such as the airframe of the FC-31 Gyrfalcon was similar to the F-35.

According to IHS Jane's Defence Weekly: "The similarity includes the use of two tracking mirrors and a flat-facetted optical window, with bottom fuselage placement just aft the radar radome." 

Even though the J-31 fighter made its maiden flight in late 2012 and was brought to the public in late 2014 during China's International Aviation Aerospace Exhibition, it was only during the Dubai Air Show that it was showcased for the first time overseas, according to China Military Online.

The Aviation Industry Corporation of China (AVIC), which is aggressively pushing the FC-31 as a competitor to the F-35 Joint Strike Fighter (JSF), also has seen "some interest" from  Iran and Pakistan besides the Chinese Air Force.

During the Dubai Air Show,  Li Yuhai, deputy general manager of AVIC told the press that "the FC-31 is better than any other fighters of the same class." 

"No matter it is in terms of the cost of a single fighter or in terms of the cost throughout a fighter's whole life cycle,  That is to say, the fighter's performances are not bad and it's also highly cost effective," Li said.