FILE PHOTO: Vlad Tenev, co-founder and co-CEO of investing app Robinhood, speaks during the TechCrunch Disrupt event in Brooklyn borough of New York, U.S., May 10, 2016. REUTERS/Brendan McDermid

(Reuters) - Commission-free stock trading startup Robinhood instructed some users to change their passwords on Wednesday, after discovering a logging error that left some customer credentials vulnerable, according to a company email.

“On Monday night, we discovered that some user credentials were stored in a readable format within our internal systems,” said the email seen by Reuters. The issue has been resolved, the firm said.

Robinhood, based in Menlo Park, California, said it found no evidence that the information was improperly accessed. The company declined to say how many users were affected.

“We take our responsibility to customers seriously and place an immense focus on working to ensure their information is secure,” spokesman Dan Mahoney said in a statement.

Lawmakers have been calling for stricter legislation to protect sensitive consumer data following high profile breaches at companies including Equifax Inc and American Express Co.

Equifax has agreed to pay up to $700 million to settle claims it broke the law during a massive 2017 data breach and to repay harmed consumers.

Robinhood’s commission-free stock trading app is gaining popularity among young consumers. It is one of several young companies aiming to compete with traditional financial institutions by offering cheaper and more user friendly digital services.