Natural gas pipeline operators in the United States have reportedly been the target of sophisticated phishing attacks since last year, and the Department of Homeland Security has been helping firms deal with incidents since March. “DHS’s Industrial Control Systems Cyber Emergency Response Team has been working since March 2012 with critical infrastructure owners and operators in the oil and natural gas sector to address a series of cyber intrusions targeting natural gas pipeline companies,” DHS spokesman Peter Boogaard told CNET on Tuesday. “The cyber intrusion involves sophisticated spear-phishing activities targeting personnel within the private companies. DHS is coordinating with the FBI and appropriate federal agencies, and ICS-CERT is working with affected organizations to prepare mitigation plans customized to their current network and security configurations to detect, mitigate and prevent such threats.”

The agency has been meeting with and advising companies privately and last week issued its first public warning. The DHS said that at least three confidential “amber” alerts have been issued beginning March 29th, all warning of a “gas pipeline sector cyber intrusion campaign” against multiple pipeline companies.

“ICS-CERT has recently identified an active series of cyber intrusions targeting natural gas pipeline sector companies,” an April 13th alert warned. “Multiple natural gas pipeline organizations have reported either attempts or intrusions related to this campaign. The campaign appears to have started in late December 2011 and is active today.”

The origins of the various attacks are unknown, and it is unclear if sensitive data has been compromised or if other negative consequences have resulted from the breaches. There are concerns that an employee can be tricked into opening a malicious link or download an attachment containing malware that might allow attackers to steal sensitive information, or even worse, manage to access the systems for controlling gas compressors or bulk power switching.

There are approximately 200,000 miles of interstate natural gas pipelines, which supply 25% of the nation’s energy.