For more than two years, pro-Iranian hackers have penetrated some of the world’s most sensitive computer networks, including those operated by a US-based airline, auto maker, natural gas producer, defense contractor, and military installation, security researchers said.

In many cases, “Operation Cleaver,” as the sustained hacking campaign is being dubbed, has attained the highest levels of system access of targets located in 16 countries total, according to a report published Tuesday by security firm Cylance. Compromised systems in the ongoing attacks include Active Directory domain controllers that store employee login credentials, servers running Microsoft Windows and Linux, routers, switches, and virtual private networks. With more than 50 victims that include airports, hospitals, telecommunications providers, chemical companies, and governments, the Iranian-backed hackers are reported to have extraordinary control over much of the world’s critical infrastructure. Cylance researchers wrote:

Perhaps the most bone-chilling evidence we collected in this campaign was the targeting and compromise of transportation networks and systems such as airlines and airports in South Korea, Saudi Arabia and Pakistan. The level of access seemed ubiquitous: Active Directory domains were fully compromised, along with entire Cisco Edge switches, routers, and internal networking infrastructure. Fully compromised VPN credentials meant their entire remote access infrastructure and supply chain was under the control of the Cleaver team, allowing permanent persistence under compromised credentials. They achieved complete access to airport gates and their security control systems, potentially allowing them to spoof gate credentials. They gained access to PayPal and Go Daddy credentials allowing them to make fraudulent purchases and allow[ing] unfettered access to the victim’s domains. We were witnessed [sic] a shocking amount of access into the deepest parts of these companies and the airports in which they operate.

Tuesday’s 86-page report relies on circumstantial evidence to arrive at the conclusion that the 20 or more hackers participating in Operation Cleaver are backed by Iran’s government. Members take Persian handles such as Salman Ghazikhani and Bahman Mohebbi; they work from numerous Internet domains, IP addresses, and autonomous system numbers registered in Iran; and many of the custom-configured hacking tools they use issue warnings when their external IP addresses trace back to the Middle Eastern country. The infrastructure supporting the vast campaign is too sprawling to be the work of a lone individual or small group; it could only have been sponsored by a nation state.