Companies behind the Israeli Iron Dome missile shield have reportedly been robbed off hundreds of sensitive documents by hackers from China.
Chinese government has been accused of being responsible for the attack, carried out by a hacking group Comment Crew, which reportedly started in 2011.
The information was revealed on Tuesday by a US-based security expert Joseph Drissel, a CEO of Cyber Engineering Services (CyberESI).
According to Drissel, the hackers managed to get their hands on complete rocket designs developed by defence contractors including Elisra Group, Israel Aerospace Industries and Rafael Advanced Defense Systems.
Specifications for the the Arrow III system were among the stolen materials Drissel said his company had managed to find while uncovering the attack.
Much of the technology for these systems was developed by Boeing and other contractors for use in US weapons.
"'Comment Crew' is so named for a very specific reason: They insert malware with hidden comments on various public web pages they control and use those sites as command and control centres to download stolen documents," Drissel said.
CyberESI identified these sites and was able to secure evidence of the stolen documents before Comment Crew could cover their virtual tracks, he said.
In an article on Krebs on Security, a blog operated by former Washington Post security reporter Brian Krebs, Drissel said he was disclosing the attacks only now, after years of unsuccessful attempts to persuade the affected companies and US and Israeli government authorities to address both the security issues that led to the breaches and evaluate which weapon systems may have been compromised
However, the affected companies involved denied any knowledge of such an incident.
An official at Rafael Advanced Defense Systems, who declined to be identified by name, said of the report: "Rafael does not recall such an incident. Rafael's databases, including its air defence databases, are extremely well protected."
Israel Aerospace Industries issued a statement saying that "the information reported regarding the leakage of sensitive information is incorrect." The firm maintained its "cyber security systems operate in accordance with the most rigorous requirements and also in this case they were proven to be effective."
Elistra Group didn't comment on the revelations.
The three companies are behind the Iron Dome missile shield system that now partially insulates Israel from rocket barrages fired from the Gaza Strip.
Israeli and US officials have said Iron Dome systems are responsible for shooting down more than 90 per cent of the rockets they have engaged, while ignoring missiles on a trajectory to fall wide. That accounts for about a fifth of the rockets Israel has said Palestinian militants have fired into the country during the Gaza Strip crisis.
A former senior Israeli military official said assertions that these key defence contractors had been hacked would fit with a pattern of military and industrial espionage around the globe.
"The Chinese have been doing that to all defence contractors in the West, so if this really happened, we are not alone," said Uzi Rubin, a former head of missile defence at Israel's Defense Ministry and now head of the Rubicon consultancy firm.
"If the Chinese really did it, maybe we shall see a Chinese Iron Dome in the future. It is said that imitation is the sincerest form of a compliment."
Chinese officials were not immediately available for comment.