Is this really a fact? So many fake news now are spreading on internet nowadays. But if this is true I guess that it will take effect on ethereum price. But I hope it doesn't! it's now being second of the most valuable cryptocurrency so I hope it won't happened again, I really hated hackers!

This can be true, I am not sure about value 300$ Million - but I read about Parity dev. that accidentally mess with multi-signature wallets and locked funds. Funds are frozen for now until the solution is found to fix this problem.
I think this Dev. will also be demoted, and work for parity without access wallets and blockchain for sure.
http://www.zdnet.com/article/ethereum-user-accidentally-exploits-major-vulnerability-locks-wallets