Chegg, a technology giant specializing in textbook rental, has confirmed a data breach affecting some 40 million customers.

In a filing with the Securities and Exchange Commission, the company said it will reset all user passwords after hackers gained access to the company’s customer database. That database includes users for Chegg’s website but also other products, such as citation service EasyBib, which it owns.

The breach occurred in April, but was only discovered a week ago.

Hackers stole usernames, email addresses, shipping addresses and hashed passwords, the company said, but doesn’t believe that financial data was taken.

The company went public in 2013, and is currently worth $3.3 billion. Chegg’s stock is down more than 10 percent a day after the breach was revealed.