Hackers now have possession of EBay customer names, account passwords, email addresses, physical addresses, phone numbers and birth dates.
The company picked up on the breach two weeks ago, after discovering some employee credentials were stolen.
Officials say the information theft happened two months ago, and is asking all customers to reset their passwords as a precaution.
EBay's subsidiary, PayPal, was not affected by the data breach.
The company says it has not spotted any increase in fraudulent activity on EBay so far.