Michela Menting, cybersecurity director at technology market experts ABI Research has suggested that hackers gained eBay credentials through "social engineering," a type of psychological manipulation to get people to divulge confidential information.
Menting said: "Finally I think their timely public announcement - two weeks after discovery - helps to reassure not only public opinion, but also their own brand reputation.
"Transparency when dealing with incident response for an event that has affected customers, in this case millions, is highly commendable - it means that eBay takes security seriously."
More top news
A man from China has set a rather unenviable new world record - by covering himself in more than 1.1 million bees, weighing 17st.
Chinese goalkeeper Sui Weijie has been fined 50,000 yuan (£5,240) after allowing an opponent to score while he sipped on a bottle of water
A "caring and loving" teenage boy who "lit up the life" of everyone he met has died in hospital after taking what he thought was ecstasy.