"It tells you that more than likely the attackers were pretty sophisticated," he said. "They're using some new technique, or variation of older techniques to bring the sites down."
None of the banks have given details of the attacks.
Ideologically motivated hacktivism was the primary motivation behind DDoS attacks last year, according to Arbor Networks' annual survey of Internet Service Providers. The number of high-bandwidth DDoS attacks increased significantly, with 25% exceeding the total bandwidth into a data center.
At the same time, there are a variety of DDoS attack tools and services available in the underground, Arbor said.
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