"You can never fend off all of the mice, but you can make sure the cheese is safe," he said.
The origin of the attackers in the South Korea companies is not known. The country's longtime enemy, North Korea, is a suspect. Other experts say code used in the malware is distinctly Chinese.
Wherever the origin, the attackers were not looking to steal information, but raise havoc, much like the Cyber Fighters of Izz ad-Din al-Qassam, an Islamic group that has launched distributed denial of service (DDoS) attacks in waves against major U.S. banks over the last seven months. Targets included Bank of America, PNC Financial, Capital One Financial, JPMorgan Chase and Citigroup.
While there's no known connection between the attacks, they show how criminals will adopt different strategies, depending on what they want to accomplish. The DDoS attacks on U.S. banks were more advanced technically, but the attackers of the South Korean banks did much more damage.
"At the end of day, the sophistication doesn't particularly matter," said Dan Holden, director of security research at Arbor Networks. "The motivation dictates how sophisticated the attack needs to be."
In the U.S. bank attacks, the motivation appears to be a continuous harassment and constant probing for weaknesses in the bank's online systems. In South Korea, onetime destruction was the goal.
The third wave of attacks against the U.S. bank started again this month after a one-month suspension. In the latest assault, the attackers are constantly changing targets at the application layer of the website, rather than focus on just one for a period of time, Holden said. The format of the bogus data sent to try to overwhelm Web servers is also changing constantly.
In addition, the number of compromised servers spewing data has increased by 50% since the last attacks, Holden said. He declined to give exact numbers.
The banks have managed to fend off the attacks, suffering short periods of downtime at worse. Nevertheless, the attacks have forced the banks to spend more money to defend their systems, Holden said.
The group says the attacks will continue until YouTube removes all versions of an anti-Islam video that mocked the Prophet Muhammad. The video, called the Innocence of Muslims, sparked violent demonstrations last year in many Middle Eastern countries.
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