The Dallas pipeline company Energy Transfer Partners notified oil and gas shippers on Monday that the data system for its extensive pipeline network was hacked by still unknown cyber criminals.

The attack Energy Transfer described in a shipping notice on Monday didn’t affect its pipeline systems, the company told Bloomberg. The attack was limited to the electronic data interchange system that facilitates transactions over oil and gas moving through its pipelines and was directed at the contractor that manages the system, Latitude Technology, according to the company.

Neither Energy Transfer nor Latitude responded to requests for comment.

Over the past two years, the U.S. energy industry and other companies that operate so-called critical infrastructure such as chemical and manufaturing plants have seen a significant increase in cyberattacks targeting individuals with access to control systems that operate facilities, federal agencies and cybersecurity experts say. [read more]