EBay warned its 145 million users to change their passwords after a cyberattack that occurred three months ago that led to compromised customer data.

The cyberattack, performed by unknown hackers, happened between late February and early March. The stolen data included email addresses, encrypted passwords, mailing addresses and birth dates, among other pieces of customer information. The breach was only discovered in early May.

The multinational Internet corporation clarified that no financial data, such as credit card information, were compromised during the attack. These data remained secure because most of the payments for transactions come from Paypal, which uses separately encrypted information.

EBay spokeswoman Amanda Miller clarified that the company is making the request "out of an abundance of caution" and that it is using sophisticated, proprietary hashing and salting technology to protect the passwords. The company assured its users that fraudulent activity did not increase after the initial attack, and that they were investigating the issue with help from law enforcement and security experts, Reuters reported.

The company did not give out specific information about the attack, such as the identity of the hackers and the method used to gain entry to the system. The only statement released by the company was that the hackers somehow procured login credentials from a few employees, which gave them access to EBay's corporate network.

The company did not have the exact number of users affected, though it estimated that 145 million user accounts were compromised. EBay spokeswoman Kari Ramirez said to Reuters, "For the time being, we cannot comment on the specific number of accounts impacted. However, we believe there may be a large number of accounts involved."

Meanwhile, EBay hired FireEye Inc's Mandiant forensics division to help with the investigation. She also explained why they failed to notify users immediately of the issue.

"We worked aggressively and as quickly as possible to insure accurate and thorough disclosure of the nature and extent of the compromise," Miller told CBC News.