In a brief statement filed with government regulators on Thursday, Halliburton said it became aware of unauthorized access to its systems on Wednesday and responded by “proactively taking certain systems offline.” The company said it is “working to identify any effects of the incident.”

Halliburton, which has close to 48,000 employees in dozens of countries per company filings, is one of the world’s largest energy companies. The U.S. energy giant is widely associated with the massive oil spill caused by the Deepwater Horizon oil rig explosion in the Gulf of Mexico in 2010, in which Halliburton later agreed to settle with the U.S. government for $1.1 billion.