Websites of the Nasdaq and BATS stock exchanges, together with the Chicago Board Options Exchange (CBOE), were offline earlier this week after a hacktivist group with apparent Anonymous ties targeted them with distributed denial of service (DDoS) attacks. But while customers were intermittently unable to use some of the exchanges' websites, all said that their trading systems weren't affected.
The attacks had been previewed the day before they were launched. In a post to Pastebin, a group calling itself "the 'L0NGwave99' cyber group" said Sunday it was going to launch "Operation Digital Tornado" in support of the "99% movement" Monday at 9 a.m. New York time. A later message promised the same for Tuesday.