The DAO contract was attacked on 17th June 2016 where the attacker drained about USD 50 million worth of ethers using a recursive call vulnerability in The DAO contract code. Please find below how to get back your invested funds.
Following the attack, Ethereum community, miners and exchanges leading the vote, decided to go hard-fork. After some code change and the upgrade of Ether clients, the hard-fork was completed on July 20th. Nearly 12 million ETH have been from the “Dark DAO” and “Whitehat DAO” contracts into the WithdrawDAO recovery contract.