MADISON, Wis. -

It is among the largest Internet security breaches in history and may affect 145 million people. E-commerce company eBay said hackers breached its customer database and stole email addresses, passwords and personal information.

EBay is asking all customers who bought or sold anything within the last 12 months to immediately change their password.

"You mainly want to go in and change your password because that's the big thing," Mike Masino, an information security instructor at Madison College, said. "(Hackers) got the hash password, which means they can go through and ... crack the passwords and associate passwords with a user account. Then they can go into the account and could theoretically purchase things as that person."

EBay said the hackers did not gain access to customer credit card information. Financial and credit card information is stored separately in encrypted formats.

According to eBay, hackers compromised the log-in credentials of a small number of eBay employees to gain access to the network.

This is the latest in a series of high profile security breaches. Last December hackers stole the personal information of an estimated 70 million Target customers and the debit and credit card data of 40 million customers.

Dealing with these cyber attacks is an ongoing issue.

"The threats are emerging, so you secure what you know about and then you actually learn about new things, you react and you secure those," Masino said. "Is it 100 percent? No. It is getting better and better over the years, but at the same time that we're better securing these assets, the people who attack them are getting better."

Masino recommends changing online passwords every couple months and selecting passwords that are difficult for a hacker to guess. He also recommends monitoring online accounts regularly to watch for unusual activity.