WASHINGTON—Chinese spies used code first developed by the U.S. National Security Agency to support their hacking operations, Israeli researchers said on Feb. 22, in another indication of how malicious software developed by governments can boomerang against their creators. Tel Aviv-based Check Point Software Technologies issued a report noting that some features in a piece of China-linked malware it dubs “Jian” were so similar they could only have been stolen from some of the National Security Agency break-in tools leaked to the internet in 2017. Yaniv Balmas, Checkpoint’s head of research, called Jian “kind of a copycat, a Chinese replica.” The find comes as some experts argue that U.S. spies should devote more energy to fixing the flaws they find in software, instead of developing and deploying malicious software to exploit it. The NSA declined to comment. The Chinese Embassy in Washington didn’t immediately respond to requests for comment. Lockheed Martin …