Schools across the Pittsburg Unified School District were struck by a ransomware attack during the winter break, shutting down the district’s email and server for a period of time, school officials said Monday.

Superintendent Janet Schulze said the jeopardized servers were immediately taken offline. School officials, who were working with two external information technology firms and lawyers, had no indication that any personal data or information had been compromised. Classes were scheduled to resume on Tuesday for most schools across the district.

Generally in a ransomware attack, hackers infiltrate a computer network, lock it down and then demand a “ransom” before the system will be released. It appears the attack is still impacting the school.

“We will be teaching and learning like ‘back in the day’ ... without laptops and Internet,” Schulze said in a statement posted on Facebook. “We are continuing to investigate and work with a cybersecurity team and experts. Since the investigation is continuing, complete findings are not available and it is still too early for us to provide further details.”

School officials said they had notified authorities of the attack. A message left at the superintendent’s office was not immediately returned Tuesday.

Alejandro Serrano is a San Francisco Chronicle staff writer. Email: alejandro.serrano@sfchronicle.com Twitter: @serrano_alej