Hackers have accessed American election systems, the FBI and Cybersecurity and Infrastructure Security Agency (CISA) said in a joint statement Wednesday.
The CISA, which is part of the Department of Homeland Security, said that while government networks were accessed, including "unauthorized access to elections support system", there is "no evidence to date that integrity of elections data has been compromised."
The hackers used “vulnerability chaining" in which they exploited several vulnerabilities in the systems to gain access, including a Virtual Private Network (VPN) vulnerability and a flaw in the Windows Netlogon protocol.
The affected networks include federal and state, local, tribal, and territorial government networks, critical infrastructure, and elections organizations.
The statement referred to the hackers as "advanced persistent threat (APT) actors," a term which experts say is usually reserved for state-sponsored hacking units.
Last month, Microsoft stated that it had discovered actors from Russia, China and Iran targeting the US Presidential Election which will be held next month.