American officials have said that U.S. has considered delivering a formal warning through diplomatic channels but has not pursued the idea out of fears that doing so could escalate hostilities.
U.S. intelligence officials have said they believe the disruptions, called distributed denial of service (DDOS) attacks, are the work of the Iranian regime.
More worrisome to the government and banking officials are destructive attacks that corrupt financial data or cause panic that can harm the economy.
In one of the most damaging such incidents, a cyberattack last summer wiped data from computers at Saudi Arabia’s state-owned oil company Saudi Aramco, rendering them inoperable. U.S. intelligence officials have said they believe Iranian regime was also behind that attack.
In a speech last fall, then-Defense Secretary Leon E. Panetta called it “probably the most destructive” cyberattack launched against the private sector to date.
That speech, analysts said, was a veiled warning to Iran that the United States would not accept destructive attacks on its critical computer systems.
The report says the disruptions reflects the pressure the administration is under from banking industry officials, who want to know what amount of pain or damage will justify a government response.
“We don’t have a clear view of what are the triggers — and we’ve asked,” said one industry official who has been involved in discussions with the administration and who spoke on the condition of anonymity. “They’ve just been very coy about it.”