PEOPLE HAVE DONE BAD THINGS with computers for decades. Even before personal computers, people (“phreakers”) used to abuse telephone systems. The hacking journal 2600 takes its name from the 2600Hz tone required to trick AT&T phone lines into giving free calls in the 1960s. This was possible because the same line carried both voice and connection-management signals.
Such in-band signalling was done away with in the 70s when a new signalling system was introduced. This enabled different networks to send this data out of band. This system, known as SS7, is still in use today, and is vulnerable to a manin-the-middle attack. This has been exploited to allow second-factor SMS codes to be intercepted, and accounts to be compromised.