It advised customers to change their passwords immediately, saying they were among the pieces of data stolen by cyber criminals who carried out the attack between late February and early March.
EBay spokeswoman Amanda Miller told Reuters those passwords were encrypted and that the company had no reason to believe the hackers had broken the code that scrambled them.
"There is no evidence of impact on any eBay customers," Miller said. "We don't know that they decrypted the passwords because it would not be easy to do."
She said the hackers copied a massive user database that contained those passwords, as well as email addresses, birth dates, mailing addresses and other personal information, but not financial data such as credit card numbers.
The company had earlier said a large number of accounts may have been compromised, but declined to say how many.