The Department of Homeland Security is urging natural gas pipeline operators to look out for suspicious emails, reported The Christian Science Monitor. The agency said they are part of an organized cyber attack that began five months ago.

DHS described the emails as "convincingly crafted" to seem like they were sent from someone inside the company. It's what is known as "spear-phishing."

DHS is trying to determine the scope of the attacks and said Canadian pipeline operators are targets too.

DHS has sent more details to the industry in confidential alerts and is recommending ways to mitigate the attack and get rid of the infection.

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