Network Integrity Systems Identifies Unlit Fiber Strands as a Primary Eavesdropping Pathway
NIS urges security teams to account for unused fiber entering sensitive spaces
HICKORY, N.C., – Network Integrity Systems Inc. (NIS) is identifying unused optical fiber as a primary pathway for Eavesdropping over Fiber (EoF), a technique that uses installed fiber to capture nearby conversations. The company recommends that organizations include these unlit strands in security assessments of facilities where sensitive discussions take place.
Known as dark fiber, these strands carry no network traffic but can still provide an optical path into a secure room. According to NIS, an attacker with access to one end of a suitable strand can inject sensing light and use the fiber to detect acoustic vibrations without connecting to the organization’s network equipment.
That access point may be outside the facility’s security boundary, such as a junction box, manhole or carrier vault. NIS is prepared to demonstrate the capability for members of the press, showing firsthand what a single unlit strand can pick up from a room.
Spare fiber is routinely installed for future capacity and may remain unused for years. NIS warns that strands terminating in sensitive spaces can be overlooked when security reviews focus on active data connections.
A review of unused fiber should establish where each strand terminates, whether it reaches a space used for sensitive conversations and where someone could gain access to its opposite end. These pathways may extend beyond the areas covered by a facility’s physical security controls. Accounting for them gives security personnel a clearer basis for deciding which strands require monitoring and investigating unexpected optical activity on fiber that should remain dark.
Research presented at the NDSS Symposium 2026 demonstrated acoustic eavesdropping through telecom fiber using commercially available Distributed Acoustic Sensing equipment and a sensory receptor to improve sound capture. Performance depends on cable construction, installation conditions and the acoustic environment. NIS reports that its own independent demonstrations have recovered clear conversations.
To detect this activity, NIS developed InLighten, technology that continuously monitors dark fiber for unauthorized sensing light and alerts security personnel to a potential eavesdropping attempt. InLighten Mobile provides a handheld option for testing individual strands. Monitoring requires the fibers to be identified and connected to the detection system.
InLighten is protected by U.S. Patent Nos. 12,615,084, 12,706,682 and 12,739,039, with additional EoF mitigation applications pending. NIS offers confidential briefings and demonstrations for organizations assessing their exposure. More information is available at networkintegritysystems.com.
About Network Integrity Systems
Founded in North Carolina in 2003, Network Integrity Systems develops optical sensing technologies that protect classified networks, critical infrastructure and other mission-critical assets. NIS technology continuously monitors fiber-optic cables, pathways and vulnerable access points for activity that may indicate tapping, tampering, intrusion, infrastructure damage or other physical cyber threats. Product lines include INTERCEPTOR for U.S. government and defense, VANGUARD for private enterprise, SENTINEL for perimeter and asset protection, INLIGHTEN for eavesdropping detection, and INSIGHT for alarm response and management. NIS is headquartered in Hickory, North Carolina. Confidential briefings and demonstrations are available on request.
Network Integrity Systems Inc.
1937 Tate Blvd. SE, Hickory, NC 28602
828.322.2181
