Detecting and Preventing Eavesdropping

Any indication that an adversary or competitor is using illegal means to collect information should alert you to the possibility, at least, that listening devices might be planted in your office or home. There are a number of specific warning signs that you may be the target of eavesdropping. Of course, if eavesdropping is done by a professional, and done correctly, you may not see any of these signs.

One of the most common indicators of eavesdropping is that other people seem to know something they shouldn’t know. If you learn that an activity, plan, or meeting that should be secret is known to an adversary or competitor, you should ask yourself how they might have learned that.

An eavesdropper will often use some pretext to gain physical access to your office or home. It is easy for an outsider to gain access to many office buildings by impersonating a technician checking on such things as the air conditioning or heating. The only props needed are a workman’s uniform, hard hat, clipboard with some forms, and a belt full of tools. If challenged, the imposter might threaten not to come back for three weeks because he is so busy. In one version of this technique, the eavesdropper actually causes a problem and then shows up unrequested to fix it. In other words, you must verify that anyone performing work in or around your office was actually requested and is authorized to do this work. If a worker shows up without being asked, this suggests an attempted eavesdropping operation and should be reported immediately to your security office. Even when the work is requested, outside service personnel entering rooms containing sensitive information should always be accompanied and monitored.

Gifts are another means of infiltrating a bug into a target office. Be a little suspicious if you receive from one of your contacts a gift of something that might normally be kept in your office -- for example, a framed picture for the wall or any sort of electronic device. Electronic devices are especially suspicious as they provide an available power supply, have space for concealing a mike and transmitter, and it is often difficult to distinguish the bug from other electronic parts. Have any gift checked by a technical countermeasures specialist before keeping it in a room where sensitive discussions are held.

Unusual sounds can be a tip off that something is amiss. Strange sounds or volume changes on your phone line while you are talking can be caused by eavesdropping. However, they can also be caused by many other things and are relatively common, so this is not a significant indicator unless it happens repeatedly. On the other hand, if you ever hear sounds coming from your phone while it is hung up, this is significant and definitely should be investigated. If your television, radio, or other electrical appliance in a sensitive area experiences strange interference from some other electronic device, this should also be investigated if it happens repeatedly.

Illegal entry to your office or home to install an eavesdropping device sometimes leaves telltale signs, especially if done by an amateur. Evidence of improper entry with nothing being taken is suspicious. Installing an eavesdropping device sometimes involves moving ceiling tiles, electrical outlets, switches, light fixtures, or drilling a pinhole opening in the wall or ceiling of the target room (drilling in from the other side of the wall or ceiling). This can leave a small bit of debris, especially white dry-wall dust that should not be cleaned up. It should be reported to the security office. 

In summary, protection against the installation of eavesdropping devices requires:

  • Alert employees.
  • Round the clock control over physical access by outsiders to the area to be protected.
  • Continuous supervision/observation of all service personnel allowed into the area for repairs or to make alterations.
  • Thorough inspection by a qualified technical countermeasures specialist of all new furnishings, decorations, or equipment brought into the area.

What to Do if You Suspect
You Have Been Bugged

If you suspect you are bugged, do not discuss your suspicions with others unless they have a real need to know. Above all, do not discuss your suspicions in a room that might be bugged. Do not deviate from the normal pattern of conversation in the room. Advise your security officer promptly, but do not do it by phone. The bug may be in the telephone instrument. Do it in person, and discuss the problem in an area that you are confident is secure.

These security measures are important to ensure that the perpetrator does not become aware of your suspicions. A perpetrator who becomes aware you are suspicious will very likely take steps to make it more difficult to find the device. He may remove the device or switch it off remotely.

bullet  Never try to find a bug or wiretap yourself. What’s the point? If you are suspicious enough to look, you already know you should not have any sensitive conversation in that room. If there is a bug there, do-it-yourself approaches probably will not find it. If you look and don’t find it, that certainly shouldn’t give you any sense of confidence that you can speak freely in that room. Don’t be misled by what you see on television, in the movies, or in spy-shop catalogs. Detecting bugs is difficult even for the professionals who specialize in that work.

Technical Security Countermeasures

A Technical Security Countermeasures (TSCM) survey, also known as a "sweep," is a service provided by highly qualified personnel to detect the presence of technical surveillance devices and hazards and to identify technical security weaknesses that could facilitate a technical penetration of the surveyed facility. It consists of several parts.1

  • An electronic search of the radio frequency (RF) spectrum to detect any unauthorized emanations from the area being examined.
  • An electronically enhanced search of walls, ceilings, floors, furnishings, and accessories to look for clandestine microphones, recorders, or transmitters, both active and quiescent.
  • A physical examination of interior and exterior areas such as the space above false ceilings and heating, air conditioning, plumbing, and ventilation systems to search for physical evidence of eavesdropping.
  • Identification of physical security weaknesses that could be exploited by an eavesdropper to gain access to place technical surveillance equipment in the target area.

During the survey, TSCM team members may enter office areas where employees are working. Employees should be advised in writing, not orally, that a technical security inspection is being conducting and that they should not discuss it in the office before, during, or after the survey

1. This section is based on an article by James Calhoun, "Clear the Air with TSCM." Department of Defense Security Institute, Security Awareness Bulletin 2-96. The article appeared previously in Security Management magazine.


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