Computers at the FBI’s New York office were hacked in what the agency said was a now-contained isolated incident, CNN reported , citing people briefed on the matter.

“The FBI is aware of the incident and is working to gain additional information,” the bureau said in a statement to CNN, adding that its investigation of the malicious cyber activity is ongoing.

“This is an isolated incident that has been contained.”

It was not immediately clear when the cyber incident occurred. One source told CNN the origin of the incident is still being investigated.

Representatives for the Federal Bureau of Investigations could not be immediately reached for comment on the report.

CNN, citing two sources briefed on the matter, said FBI officials believe the incident involved bureau computers used to investigate child sexual exploitation.