Barracuda, a network and email security company, disclosed today that a recently patched zero-day vulnerability has been used for at least seven months to install specialised malware on customers' Email Security Gateway (ESG) equipment and steal data. According to the business, a continuing investigation revealed that the issue gave attackers access to a portion of ESG equipment and installed backdoors that gave them ongoing access to the affected systems. Additionally, Barracuda found proof that the threat actors stole data from the backdoored ESG appliances. The company fixed the problem by installing a security patch on all ESG appliances and, a day later, by deploying a specialised script, blocking the attackers' access to the compromised devices.