Network Integrity Systems Names a New Threat Class: Eavesdropping over Fiber

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NIS defines EoF as the covert use of installed optical fiber as an acoustic sensor, separating it from conventional fiber tapping and giving press, standards bodies and security practitioners a citable term.
Hickory, United States - Sept 11, 2026 - Network Integrity Systems Inc. (NIS) [https://www.networkintegritysystems.com/] has introduced Eavesdropping over Fiber, abbreviated EoF, as the name for a threat class that current security vocabulary does not cover. NIS defines EoF as the covert use of an installed optical fiber as an acoustic sensor. Sensing light is injected into the fiber from an access point that may sit well outside the protected space, and the returning or transmitted light is analyzed for the minute vibrations produced by speech near the cable. The fiber is the microphone.

To address this threat, the company is also introducing InLighten [https://www.networkintegritysystems.com/inlighten-network-integrity-systems], patented NIS technology built to detect the light an eavesdropper must inject to make a fiber listen. NIS offers the definition for citation by journalists, standards organizations, accreditation authorities and security practitioners.

"Fiber tapping" has long carried nearly every threat aimed at an optical cable: the bend coupler, the splice, the splitter dropped into a manhole. Each of those attacks goes after data moving through the glass. Recent research has demonstrated something else, which is that a fiber carrying no traffic at all can be made to listen to the surrounding room.

Two elements distinguish EoF from every neighboring technique.

First, the sensor is the cable already installed in the building, and the adversary brings no microphone to the target. Second, the collection equipment sits away from the protected space, at a demarcation point, junction box, manhole, carrier vault or central office.

Several established techniques involve both fiber and eavesdropping without meeting that definition. Optical data tapping bends, splices or splits an active fiber and captures a fraction of the transmitted light, stealing the communications traveling through the cable instead of hearing conversations beside it. Optical and laser microphones direct light at a vibrating window or other reflective surface and reconstruct room audio from the reflected beam, a form of optical eavesdropping in which the building fiber plays no part. Purpose-built fiber-optic microphones require a transducer assembly, such as a diaphragm, interferometer or reflector, deliberately installed and connected to fiber. Conventional bugs that use fiber for transport rely on a hidden microphone to collect the sound, leaving the fiber to carry the audio. EoF covers the case where the installed fiber itself is the sensing element and no microphone is introduced into the protected space.

The underlying phenomenon has a long and well-documented lineage, and NIS makes no claim otherwise. Fiber-optic acoustic sensing experiments trace back to the 1970s. End-to-end interferometry transmits a laser through an ordinary fiber and measures changes in phase or intensity at the far end. Vibrations affecting the fiber, including sound, can be detected this way from a remote location, and interferometric interrogation remains available to an adversary today. What it generally cannot do is localize, because the measurement describes the fiber collectively and does not identify where along the strand a particular sound occurred, making identifying sounds at points along the fiber difficult..

Distributed Acoustic Sensing (DAS) raises the severity considerably.

By analyzing backscattered light from rapid laser pulses, DAS adds long-range, distributed detection and the ability to place a conversation at a point along the cable. DAS remains a valuable technology used for earthquake detection, pipeline monitoring, and the protection of utilities, borders and long-haul communications routes. NIS also offers DAS-based infrastructure protection through the FOCUS product lines.

The security concern arises when that acoustic sensitivity is aimed at speech. EoF is not limited to DAS, and NIS cautions that requirements written only around DAS signatures would leave other interferometric methods outside the control; however, DAS enables the unique threat of recording specific locations along an otherwise standard fiber optic cable installed universally for data communication.

No publicly confirmed espionage operation in which an ordinary telecom fiber served as the microphone has been documented. Historical use of optical microphones, purpose-built fiber sensors and fiber data taps is well established, while covert operational use of ordinary fiber to capture nearby speech is not part of the public record.

Two research teams demonstrated the effect this year. Researchers from Hong Kong Polytechnic University and the Chinese University of Hong Kong, presenting at the NDSS Symposium 2026, recovered more than 80 percent of spoken content at a range of two meters using commercially available DAS equipment, and localized sound sources within a room to sub-meter accuracy. In a separate office test, two rooms connected by more than 50 meters of fiber, the team recovered intelligible speech even under noisy conditions.

Their method wound the fiber around a 65-millimeter cylinder to amplify the vibrations reaching the strand. In May, Science reported that a team led by Jack Lee Smith of the University of Edinburgh, presenting at the European Geosciences Union general assembly in Vienna, recovered intelligible speech from coiled fiber within about five meters of a speaker during a field test that reused an existing DAS installation built to study coastal erosion. Freely available artificial intelligence software converted the fiber data into real-time transcripts.

NIS has conducted independent research and testing into EoF. Internal demonstrations recovered intelligible conversations, confirming that the threat has advanced beyond the garbled audio associated with earlier generations of DAS equipment. Performance varies with cable construction, installation conditions, acoustic environment and signal-processing methods.

Countermeasures are written in the language available at the time of writing. Physical, acoustic and radio-frequency sweeps assume a listening device exists somewhere inside or near the protected space. EoF breaks that assumption. The cable is the sensor, the electronics are remote, and a sweep of the room may return nothing at all. The equipment also need not stay attached: an adversary can reach the fiber at a distant endpoint, connect interrogation equipment, collect, and remove it, leaving a scheduled inspection nothing to find. Classified facilities, Sensitive Compartmented Information Facilities and comparable secure environments face the gap most directly.

To use a fiber as a microphone, an adversary must inject sensing light into that fiber. InLighten detects exactly that. Placed at the edge of the secure environment, the technology continuously monitors fiber that should remain inactive and alerts security personnel when optical signals indicative of an acoustic sensing attempt appear. InLighten provides real-time visibility into whether a monitoring attempt is in progress.

Inlighten Mobile is a handheld detection device that allows for the testing of fibers.

InLighten is protected by U.S. Patent No. 12,615,084, "Securement of Optical Fibers Against Eavesdropping Using Monitoring of Signals on a Fiber," issued to NIS on April 28, 2026. Additional patent applications related to EoF mitigation are pending.

The technology complements INTERCEPTOR, the NIS Alarmed Protected Distribution System line, which protects classified network infrastructure against tapping, tampering and physical attack without using acoustic-based sensing.

NIS will demonstrate InLighten at Booth 321 during TechNet Augusta, Aug. 17-20, at the Augusta Marriott at the Convention Center in Augusta, Georgia. Confidential briefings and demonstrations covering potential exposure and EoF detection are available on request.

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.

networkintegritysystems.com [https://www.networkintegritysystems.com/]

Demonstrations are available by request. [https://hub.networkintegritysystems.com/rockcity]

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Company Name: Network Integrity Systems Inc.
Contact Person: Dave Cunningham
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Address:1937 Tate Blvd. SE, Hickory, NC 28602
City: Hickory
Country: United States
Website: https://www.networkintegritysystems.com/

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