Hackers attacked online services of Capital One, the bank said Tuesday.
A spokeswoman of the bank said all other systems were not affected by the denial of services attack.
"We have no reason to believe that customer and account information is at risk," spokeswoman Tatiana Stead said in an email to CNBC. "As always, protecting customer information is a top priority. "
She said technicians were working to restore all online services as soon as possible. Customers seeking more assistance should call the phone number on their card or statement.
Iranian hackers were suspected in a wave of cyberattacks in the past year against U.S. financial institutions, including Bank of America, JPMorgan Chase and Citigroup.