I recently found an article, written by David 
Goldman of CNN, discussing the denial of services attacks against the 
banks: Bank of America, JPMorgan Chase, Wells Fargo, US Bank, and PNC 
Bank.  Security experts say the outages stem from one of the biggest 
cyber-attacks they've ever seen. These "denial of service" attacks -- 
huge amounts of traffic directed at a website to make it crash -- were 
the largest ever recorded by a wide margin, according to two 
researchers. (Goldman, 2012)   These same banks have a great deal of 
defenses built to prevent such attacks, but Goldman says this time they 
were outgunned.  
"The
 volume of traffic sent to these sites is frankly unprecedented," said 
Dmitri Alperovitch, co-founder of CrowdStrike, a security firm that has 
been investigating the attacks. "It's 10 to 20 times the volume that we 
normally see, and twice the previous record for a denial of service 
attack."  To carry out the cyberattacks, the attackers got hold of 
thousands of high-powered application servers and pointed them all at 
the targeted banks. That overwhelmed Bank of America and Chase's Web 
servers on Sept. 19, Wells Fargo and U.S. Bank on Wednesday and PNC on 
Thursday.
Goldman
 writes, denial of service attacks are an effective but unsophisticated 
tool that doesn't involve any actual hacking. No data was stolen from 
the banks, and their transactional systems -- like their ATM networks --
 remained unaffected. The aim of the attacks was simply to temporarily 
knock down the banks' public-facing websites. That level of pre-planning
 is a deviation from the kinds of denial of service attacks launched at 
banks in the past by so-called "hacktivists." Typically, hacktivists use
 home PCs infected with malware to amass their botnets. Attacks on this 
scale would be impossible to carry out with home PCs -- users too 
frequently turn them off or disconnect them from the Internet. 
Cited:
Goldman, David. (2012). CNN: Major Banks hit with biggest cyber-attacks in history. Retrieved at: http://money.cnn.com/2012/09/