A group of cryptographers has devised a new attack against AES, the de facto standard encryption algorithm, that enables them to recover an encryption key in far less time than had been possible before. The attack can recover an AES-256 key in a small enough amount of time to make the method practical for common attackers. Bruce Schneier has seen a draft of the paper and has some of the details. Schneier said that while there s no reason to panic right now, this attack is by far the most impressive to date against AES.
Source: https://threatpost.com/new-attack-against-aes-256-huge-result-073109/73014/