The FBI is investigating suspicious cyber activity on an internal system containing sensitive surveillance information, including legal process returns and personally identifiable data from ongoing investigations. The bureau began probing abnormal log data on February 17 after detecting sophisticated techniques being used to exploit network security controls. The affected system is unclassified but contains law enforcement sensitive information.

According to a notification sent to Congress, the intrusion involves pen register and trap and trace surveillance returns - tools that log phone numbers dialed by specific lines. The attackers leveraged a commercial internet service provider vendor's infrastructure to bypass FBI network security measures. This marks the latest in a series of cyber incidents targeting federal agencies, which have long been prime targets for foreign intelligence services seeking to monitor sensitive operations.

While the FBI has addressed the immediate threat and confirmed the incident, officials have not identified the responsible parties. The breach raises fresh concerns about the security of sensitive law enforcement data and the effectiveness of current cybersecurity measures protecting federal investigative systems.