Източници
http://bg.wikipedia.org/wiki/%D0%95%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%BD%D0%BE_%D0%B1%D0%B0%D0%BD%D0%BA%D0%B8%D1%80%D0%B0%D0%BD%D0%B
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http://www.referati.org/elektronno-bankirane/16475/ref/p9
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http://www.referati.org/elektronno-bankirane/16475/ref/p9