A recent series of busts has shaken the world of dark net weapons commerce. A six-month joint investigation between law enforcement in Australia and the United States, which involved law enforcement going undercover as weapons dealers, has resulted in 17 arrests internationally.
In September 2014, the US Homeland Security Investigations (HSI) identified a 33-year-old US-based dark net seller of weapons to a worldwide client base, according to a press release from the Australian Federal Police (AFP).
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https://www.cryptocoinsnews.com/dark-net-weapons-bust-leads-17-arrests-80000-bitcoin-seizure/These things will not help bitcoin to go mainstream, I also know you can (maybe) do these things also with all the FIAT currencies... but people like to use bitcoin....
Fiat is not as digitally assessable as bitcoin and lots of these deals happen digitally so they have to use bitcoin.