(CNN) -- Hackers recently compromised the computer network of a U.S. public utility, according to a new report from the Department of Homeland Security.
"A public utility was recently compromised when a sophisticated threat actor gained unauthorized access to its control system network," according to the recently published report from the DHS' Industrial Control Systems Cyber Emergency Response Team.
The online infiltration of critical infrastructure, including power and water facilities, has become a 21st century national security concern.
In this case, the unnamed utility was able to repel the hacking, according to DHS.
"In this instance, while unauthorized access was identified, ICS-CERT was able to work with the affected entity to put in place mitigation strategies and ensure the security of their control systems before there was any impact to operations," a DHS official said.
The hackers gained access through the Internet and bypassed simple passwords through a tactic known as "brute force," according to the agency's report.
The company was not identified.
DHS works with the private sector to combat the threat of hackers and the disclosure of cyberinfiltration at a public utility is rarely made public.
In 2013, the Homeland Security Department received 181 vulnerability reports, according to the report.
"It was determined that the systems were likely exposed to numerous security threats and previous intrusion activity was also identified," the report said.
"Malicious cyberactivity targeting government and private sector networks can result in intentional and in some cases unintentional consequences, which can threaten national and economic security, critical infrastructure, as well as public health and welfare," Glenn Lemons, senior intelligence officer on cybermatters at DHS, told a congressional hearing on Wednesday.
On Monday, the Department of Justice announced the indictment of members of China's military for allegedly hacking into numerous American businesses and entities.