The IRS (US tax authority) recently released a six page document with 16 questions and answers that explain position on Bitcoin: http://www.irs.gov/pub/irs-drop/n-14-21.pdf.irs and cra on bitcoin
Our own CRA hasn’t put quite so much pen to paper but did post a fact sheet on digital currency late last year: http://www.cra-arc.gc.ca/nwsrm/fctshts/2013/m11/fs131105-eng.html.
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