U.S. Department of Energy's (DOE) computer network was hacked in January, but no classified information was compromised, U.S. media reports said Monday.

The PC Magazine said on its website that the cyber attack took place in mid-January, and resulted in the disclosure of personally identifiable information from employees and contractors.

In a Friday email sent to employees, the department said "the Department's Cybersecurity Team, the Office of Health, Safety and Security and the Inspector General's office are working with federal law enforcement to promptly gather detailed information on the nature and scope of the incident and assess the potential impacts to DOE staff and contractors," the email said.

The department said that the personally identifiable information of "several hundred" employees and contractors "may have been affected."

"As individual affected employees are identified, they will be notified and offered assistance on steps they can take to protect themselves from potential identity theft," the department said.

The Energy Department said it is "leading an aggressive effort to reduce the likelihood of these events occurring again," including a boost in network monitoring and the deployment of " specialized defense tools to protect sensitive assets," though it did not elaborate, but it urged all employees to encrypt files and emails that include sensitive information and not to email non- government personal information on department network computers.