The US government has denied that hackers were responsible for technical malfunctions at three important American institutions.

On Wednesday, the US stock exchange, United Airlines ticketing system and the website of the Wall Street Journal all went offline for hours at a time.

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“The malfunctions at United and the NYSE were not the result of any nefarious actor,” US secretary of homeland security Jeh Johnson told local media in the afternoon.

“We know less about The Wall Street Journal at this point. But their system is back up again.”

Despite this statement, there is speculation the incidents were the result of a cyberattack, mostly because of a comment posted online by a person claiming affiliation with hacking group Anonymous.

“Wonder if tomorrow is going to be bad for Wall Street,” the Twitter account said on Tuesday, before the technical glitches.

“[W]e can only hope.”

About 900 flights were initially disrupted by the United Airlines malfunction, with more delays expected.

The stock exchange outage seemed, in the main, to prevent fearful investors from selling up in panic at the financial crises in Greece and China.

The Wall Street Journal has not commented on the impact of the glitch on its website traffic.

The US is frequently targeted by Russian and Chinese hackers.

Wonder if tomorrow is going to be bad for Wall Street…. we can only hope.

— Anonymous (@YourAnonNews) July 8, 2015