The US government has warned of an al-Qaeda call to attack US online stock market and banking services.
The threat, seen on an al-Qaeda website, applied to the whole of December.
It was said to be in revenge for the continued detention of suspects at the US prison camp in Guantanamo Bay.
A spokesman for the Department of Homeland Security, Russ Knocke, said there was no evidence to corroborate the threat.
He said the US Computer Emergency Readiness team had issued a "situational awareness report to industry stakeholders".
However, he said it had been issued out of what he called "an abundance of caution".
The warning said the threat called for attacks to begin Friday and run through the month of December.
It is described as an "aspirational threat" and the nature of the warning is particularly vague, the BBC's Guto Harri in New York says.
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