Reports indicate that websites operated by Nasdaq OMX, the Chicago Board Options exchange, and Bats Trading all experienced temporary disruptions due to a spate of distributed denial of service (DDoS) attacks.
The duration of the disruptions was said to be minimal, and sources stated that the strength of the attacks has diminished significantly overnight, and that trading was not affected.
Nasdaq officials assured that systems were not compromised, stating that "the Web site wasn't hacked, nobody got any information. What they did was try to block access for our users," spokesman Joseph Christinat said.
"Our trading systems were not affected and there were no exchange customer disruptions associated with the incident," a Bats spokesperson was also quoted as saying.
A hacktivist group sympathetic to the Occupy Wall Street movement called L0NGwave99 claimed responsibility for the attacks, and issued a statement: "This DDoS Operation over NASDAQ is done in support of the great and rooted 99% movement, whom the L0NGwave99 Group has decided to give a present."
Early last year, The Wall Street Journal reported that NASDAQ network systems had been breached by hackers on multiple occasions throughout 2010.
The platform responsible for executing trades was not compromised, but systems for the exchanges Directors Desk - an online data and information sharing service - were said to have been penetrated.
The intruders did not appear to have done any damage to systems, and sources familiar with the incidents speculate that the hackers were merely doing some network reconnaissance.
Both the Federal Bureau of Investigation and the Secret Service opened investigations into the network intrusion.
"Cyber attacks against corporations and government occur constantly. NASDAQ OMX remains vigilant against such attacks," the exchange said in a prepared statement released a few dasy after the WSJ story broke.