Security researchers at Mandiant say China-backed hackers are likely behind the mass-exploitation of a recently discovered security flaw in Barracuda Networks’ email security gear, which prompted a warning to customers to remove and replace affected devices. Mandiant, which was called in to run Barracuda’s incident response, said the hackers exploited the flaw to compromise hundreds of organizations likely as part of an espionage campaign in support of the Chinese government. Almost a third of the targeted organizations are government agencies, Mandiant said in a report published Thursday. Last month, Barracuda discovered the security flaw affecting its Email Security Gateway (ESG)…