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Most people use the term "bug" when discussing the various ways in which information can be extracted from an area, . This is generally an all inclusive term which encompasses everything placed on the telephone lines. In reality, there are two different types of attack with two different names. How should they be described?

In the simplest description, a "bug" is generally an externally powered device which radiates (transmits) a signal containing intelligence, whereas a "tap" is an attachment normally made to a pair of lines for the purpose of recording or monitoring intelligence, be it audio, video or data.

In describing a "tap", generally the first thing that comes to mind is the telephone tap. As glamorized on television, it is thought of as a "drop-in" microphone which transmits the conversation taking place within a room. This method of attack is, in reality, a "bug" and not a "tap".

Also, on occasion, we see on television the eavesdropper sitting in an office or basement with headphones listening to conversations on the telephone. This is a fairly true representation of what happens, but there are more ways of "tapping". They can range from the crude attack hooking a sound-powered telephone repairmanís handset directly to the lines, to the more sophisticated method of using a high impedance device between the lines and a recorder or amplifier, to using an inductive device in which the telephone or lines are not physically altered.

If the telephone instrument has not been modified, then the only time it can be monitored is when the telephone is in actual use. However, with any one of a number of simple to sophisticated attacks, it is possible to "listen in" at all times to everything that is being said in the vicinity of the telephone.

Eavesdroppers can install in-line "series" or "parallel" transmitters on the telephone line in which no external power supplies are necessary - power is taken from the telephone lines. No antenna or microphone is required. These devices can be placed at any point along the telephone line and from the telephone to the nearest switching equipment. They can be as large as the cover on a fountain pen or they can be as small as a dime.

The operating frequency can range from as low as 30 MHz to over 1200 MHz. That is not to say this is the only range of frequencies in which they will be found, only that it is easier to build the devices to operate within these ranges.

Other attacks that can be made on the telephone include the manipulation (bending) of contacts on the hookswitch, the addition of jumpers in the telephone, or the installation of resistors or capacitors. These attacks will allow your conversations to be monitored regardless of whether the telephone is on hook or not.

The techniques discussed above are not to be considered the only attacks possible to a telephone system. They are just a representative sampling.
   
 

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