NEW YORK, May 8 (Reuters) - Top U.S. fuel pipeline operator Colonial Pipeline has shut its entire network, the source of nearly half of the U.S. East Coast's fuel supply, after a cyber attack that the company said was caused by ransomware.

The incident is one of the most disruptive digital ransom operations ever reported and has drawn attention to how critical U.S. energy infrastructure is vulnerable to hackers. The shutdown has raised fears of a price spike at gasoline pumps ahead of peak summer driving season if it persists.

Colonial 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 linking refiners on the Gulf Coast to the eastern and southern United States.

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

While the U.S. government investigation is in early stages, one former official and two industry sources said the hackers are likely a professional cybercriminal group. The former official said investigators are looking at a group dubbed "DarkSide," known for deploying ransomware and extorting victims while avoiding targets in post-Soviet states.

Colonial said the incident involved the use of ransomware, a type of malware designed to lock down systems by encrypting data and demanding payment to regain access.

Colonial has engaged a cybersecurity firm to launch an investigation and contacted law enforcement and federal agencies, it said. Read more at Reuters