A custom-built tone generator that allowed phone phreaks to seize control of the trunk lines in older analog telephone networks. By playing a precise 2600-hertz tone, the device tricked the switching equipment into thinking the line was idle and ready for routing commands. The user could then dial any number globally without the billing equipment registering the call.
They caught him wiring up a blue box in the basement to make free calls to Europe.
The vulnerability exploited by these devices forced the telecom industry to move to out-of-band signaling protocols like SS7, where control data travels on a separate channel from the voice audio.
Related terms
In-band signaling
The transmission of network control signals over the same channel used for the actual voice or data payload.
Hacker
A skilled computer expert who explores, modifies, or exploits systems and networks.
PSTN
The global infrastructure of circuit-switched telephone networks operated by national and regional carriers.