The nature of mycoin.hk's business was not clear. It apparently involved mining, and perhaps some Ponzi-like scheme. I could not tell whether it also worked as a live exchange.
Article in Chinese:
http://hk.apple.nextmedia.com/news/art/20150208/19034053
Google translation:
EDIT: See also the reddit thread. One comment in there claims that the report is incorrect.
If this turns out to be true then China or the PBOC will probably ban Bitcoin in China once and forever. With all the chinese money disappearing Bitcoin will probably crash to ~50$ according to financial bitcoin experts.
500 US$ million is more than 2 BTC million at actual price. I remember MtGox scammed only 850k BTC but at the price of the time it was 450 US$ million so quite similar in value. Not sure how to rate impact since MtGox affected more adopters than this Hong Kongese 'exchange' (it apparently affected only 30 people).
30 people with over 10 mil each lost but I am sure there are MANY others
Bitstamp is losing its bank account, another exchange "hacked"...bad news for BTC