Halliburton confirmed on Friday that it was hit by a cyberattack that forced the major oilfield services company to take systems offline.

In a filing, Halliburton said it became aware on Wednesday that an “unauthorized third party gained access to certain of its systems.”

Halliburton said it immediately “activated its cybersecurity response plan and launched an investigation internally with the support of external advisers to assess and remediate the unauthorized activity.”

That response included “proactively taking certain systems offline to help protect them and notifying law enforcement,” Halliburton said.

Halliburton, which plays a key role in maintaining the supply of oil and natural gas, did not disclose the identity of the hackers nor say whether a ransom demand has been made. The company said the investigation is “ongoing” and its response includes restoring systems and assessing the damage.

The company did not immediately respond to a request for further comment about whether its operations have been disrupted.

CNN has reached out to the FBI and the Energy Department for comment. The Cybersecurity and Infrastructure Security Agency referred questions to Halliburton.

The Energy Department told CNN on Thursday that there were no signs that energy services had been impacted.

Halliburton previously would say only that it was experiencing an “issue” without confirming or denying a Reuters report it was cyber-related.