“On March 28, American Express’ website went offline for at least two hours during a distributed denial of service attack. A group calling itself ‘the cyber-fighters of Izz ad-Din al-Qassam’ claimed responsibility for the attack, which began at about 3:00pm Eastern Time.
In a statement, an American Express spokesperson said, ‘Our site experienced a distributed-denial-of-service (DDoS) attack for about two hours on Thursday afternoon…We experienced intermittent slowing on our website that would have disrupted customers’ ability to access their account information. We had a plan in place to defend against a potential attack and have taken steps to minimize ongoing customer impact.'”
Source:“Funded hacktivism” or cyber-terrorists, AmEx attackers have big bankroll | Ars Technica