Ever since its creation in 2008, anonymous hacking groups have targeted major bitcoin exchanges and wallet platforms such as Bitstamp, successfully retrieving over five million euros worth of bitcoins from user funds and accounts.
Such incidents have followed heavy criticism against bitcoin and its viability as a currency and has played a vital role in the valuation of the currency. Earlier last year for example, the Mt. Gox heist plummeted the price of bitcoin, falling from around US$1,000 to US$200 per coin.
http://www.newsbtc.com/2015/12/24/could-bitcoin-blockchain-save-banks-from-hacking-attacks-and-theft/