Customers of JPMorgan Chase reported seeing zero balances in their accounts both online and on mobile, and speculated that the bank's systems had been hacked into.
The bank however clarified late Monday that it was having a technology problem regarding customers' balance information that it was working to resolve.
"Almost had a heart attack... Haven't checked my balance in a little bit but it read zero. Gotta be an early April Fool joke or something," wrote one user on Twitter. Some others suggested that the bank's systems may have been hacked.
"It has nothing to do with the cyber threats - it's an internal issue. We are very sorry to our customers for the inconvenience," the bank said in a statement.
"Customers are unable to view their checking account balances online and on mobile. We will keep you updated as we learn more," Chase support said in an alert on Twitter. It later said, "We're back to business as usual on Chase.com & Mobile." Chase is the U.S. consumer and commercial banking business of JPMorgan Chase.
The bank did not however disclose how many customers were affected, or what was the technical problem that affected its services.
The speculation on social networks like Twitter that the bank was hacked was probably based on DDoS (distributed denial of service) attacks that U.S. banks have faced in recent months. A group calling itself "Izz ad-Din al-Qassam Cyber Fighters," for example, launched DDoS attacks on the websites of several U.S. banks during September and October, disrupting online and mobile banking services for long periods.
The website of Chase was down about a week ago, according to reports.