Smartcard Developers Association: www.scard.org
Chaos Computer Club enlarges on SDA discoveries: www.chaos.de
For a detailed introduction to GSM security and encryption, see David Margrave's paper: www.semionoff.com/cellular/hacking/phreaking/gsm-secur.html
Report on Swiss use of GSM tracking: www.gsmag.com/oldnotw.html
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Counter Spy Shop: www.spyzone.com