This thought came to me whilst watching mr. Robot where the entire database of a financial corporation has been encrypted.
Would that (in theory) be possible if a virus was spread that would target machines in BitCoin network and encrypt the blockchain stored on these machines?
After that attackers would demand users to pay them in a new cryptocurrency which is not available for purchase yet. This would force all the users to mine their currency and (in theory) this currency would become equally as valuable as BTC since the cost would be the entire blockchain.