Ever since cryptocurrencies started gaining value, hackers have targeted exchanges that provide digital asset trading and malicious entities have siphoned billions of dollars worth of bitcoin since 2011. So far, over 1 million of the world’s BTC has been stolen from exchanges and traders continue to leave vast quantities of funds on centralized trading platforms.
https://news.bitcoin.com/hackers-have-looted-more-bitcoin-than-satoshis-entire-stash/