On 23 February 1918, German engineer Arthur Scherbius filed a patent for a rotor cipher machine that became the Enigma, marketed from 1923 by Chiffriermaschinen AG to businesses for enciphering written and telegraphic messages before transmission.
Astronomer Clifford Stoll traced a 75-cent accounting error at Lawrence Berkeley Lab to a hacker in Hannover, Germany using international X.25 network gateways to spy for the Soviet KGB.
At the 25th Chaos Communication Congress in Berlin on 27 December 2008, Tobias Engel showed that anyone with SS7 access, or a cheap commercial HLR-lookup service, could locate a mobile subscriber to roughly city level without the owner's knowledge.
On 29 December 2008 at 25C3, Erik Tews, Ralf-Philipp Weinmann and Andreas Schuler of the deDECTed.org project showed that the secret security of DECT, the standard behind most cordless phones and many baby monitors and payment terminals, could be broken with cheap hardware.
Karsten Nohl and the Chaos Computer Club published a 2-terabyte rainbow-table set at 26C3 enabling real-time over-the-air decryption of A5/1-protected 2G GSM calls and SMS with inexpensive hardware.
At 27C3 (December 2010), Harald Welte and Steve Markgraf presented OsmocomBB, a free GSM baseband stack for cheap Calypso phones, while Karsten Nohl and Sylvain Munaut used such phones to capture and decrypt GSM calls with about $15 of consumer hardware.
At IEEE Security & Privacy 2012, Driessen, Hund, Willems, Paar and Holz (Ruhr-University Bochum) published the first public analysis of the secret ciphers protecting GMR-1 and GMR-2 satellite phone calls and showed both were weak.
Tobias Engel and SRLabs demonstrated at 31C3 that SS7 design flaws allow global subscriber location tracking, call interception, and SMS 2FA theft using legally obtainable access to the signaling network.
Cybercriminals abused SS7 roaming interfaces to intercept bank-issued SMS one-time passcodes (OTPs), draining accounts of customers at O2 Germany and Metro Bank UK.
In June 2018, researchers from Ruhr University Bochum and NYU Abu Dhabi (Rupprecht, Kohls, Holz, Pöpper) disclosed that LTE user-plane traffic is encrypted but not integrity-protected, allowing a nearby man-in-the-middle relay to redirect a victim's DNS traffic.