SEATTLE — Officials for the moment say they cannot pinpoint anything malicious about the extraordinary outage of the Nasdaq stock exchange earlier today.

But the incident had all the earmarks of the three waves of denial-of-service attacks that have bedeviled U.S. financial institutions, including stock brokerages, since last September . . .

An Iranian hacking collective — Cyber Fighters of Izz ad-Din al-Qassam — has claimed credit for orchestrating sophisticated attacks that have overwhelmed the expensive security systems U.S. banks have put into place to keep their online banking services up and secure.

“My first thought is that it is a denial-of-service attack, but I’m not sure,” says Gartner banking security analyst Avivah Litan. “It’s a very attractive target. It’s very visible, and that’s what these Iranian state attacks are all about, making a political statement by disrupting a visible website.” . . .

It’s more plausible that the Iranian ideological hackers would be behind a disruption of Nasdaq, like the three-hour outage that began shortly after noon, Eastern time, Litan reasons.

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Here is a video explanation of a DDoS hacker attack: