Top U.S. fuel pipeline operator Colonial Pipeline has shut its entire network, which supplies fuel from U.S refiners on the Gulf Coast to the eastern and southern United States, after a cyber-attack that industry sources said was caused by ransomware.

The company transports 2.5 million barrels per day of gasoline, diesel, jet fuel and other refined products through 5,500 miles (8,850 km) of pipelines, and transports 45% of East Coast fuel supply.

Colonial shut down systems to contain the threat after learning of the attack on Friday, it said in a statement. That action has temporarily halted operations and affected some of its IT systems, the company said.

While the U.S. government investigation is in its early stages, one former U.S. government official and two industry sources said the hackers are most likely a highly professional cybercriminal group.

Investigators are looking into whether a group dubbed “DarkSide” by the cybersecurity research community is responsible.

DarkSide is known for deploying ransomware and extorting victims, while selectively avoiding targets in post-Soviet states.

The malicious software used in the attack was ransomware, two cybersecurity industry sources familiar with the matter said. Ransomware is a type of malware that is designed to lock down systems by encrypting data and demanding payment to regain access. The malware has grown in popularity over the last five years.

Colonial has engaged a third-party cybersecurity firm to launch an investigation and contacted law enforcement and other federal agencies, it said.

Cyber security company FireEye (FEYE.O) has been brought in to respond to the attack, the cyber security industry sources said. FireEye declined to comment when asked if it was working on the incident.

Source: Reuters