The personal information found in health care records fetches hefty sums on underground markets, making any company that stores such data a very attractive target for attackers.

"Hackers will go after anyone with health care information," said John Pescatore, director of emerging security trends at the SANS Institute, adding that in recent years hackers have increasingly set their sights on EHRs (electronic health records).

With medical data, "there's a bunch of ways you can turn that into cash," he said. For example, Social Security numbers and mailing addresses can be used to apply for credit cards or get around corporate antifraud measures.

This could explain why attackers have recently targeted U.S. health insurance providers. On Tuesday, Premera Blue Cross disclosed that the personal details of 11 million customers had been exposed in a hack that was discovered in January. Last month, Anthem, another health insurance provider, said that 78.8 million customer and employee records were accessed in an attack.

Both attacks exposed similar data, including names, Social Security numbers, birth dates, telephone numbers, member identification numbers, email addresses and mailing addresses. In the Premera breach, medical claims information was also accessed.

If the attackers try to monetize this information, the payout could prove lucrative.

Credentials that include Social Security numbers can sell for a couple of hundred dollars since the data's lifetime is much longer compared to pilfered credit card numbers, said Matt Little, vice president of product development at PKWARE, an encryption software company with clients that include health care providers. Credit card numbers, which go for a few dollars, tend to work only for a handful of days after being reported stolen.

"The bad guys are rotating around sectors," said Jeff Schmidt, CEO of IT security firm JAS Global Advisors. Other industries that are prone to attacks, such as retail and banking, have shored up their online defenses, he said. Health care, though, has lagged in IT security.

"When you get into health care, they're not fundamentally IT shops. They're not as fundamentally equipped as banking and finance to deal with these situations so you're seeing weaknesses being exploited," said Schmidt.

Medical claims information could provide attackers with another revenue stream since monetizing credit card information and Social Security numbers is "becoming increasingly difficult," he said.

The medical claim information that attackers in the Premera breach had access to could be used to blackmail victims as well, said Schmidt. Attackers could look for sensitive clinical data, like poor test results, and email patients threatening to make that information public unless they pay a ransom.

While there have been no reports that such a scenario has occurred as a result of the Premera attack, Schmidt has seen this type of blackmail in cases involving hacked executive email accounts. Premera has acknowledged being the victim of "a sophisticated cyber attack" in which the perpetrators "gained unauthorized access" to the company's IT systems but didn't "remove" any data from its systems. "To date, there's no evidence to date that such data has been used inappropriately," reads an FAQ about the attack that the company posted on its website.

When criminals try to blackmail a company, law enforcement agencies are usually called. Criminals, though, have been more successful at demanding money form individuals to keep sensitive information private, he said.

"We're never going to read about these blackmail and extortion attempts that occur as result of these breaches and it's happening all the time," said Schmidt.

Security researchers have raised the possibility that the Chinese government played a role in the Anthem and Premera breaches. The attack methods used in both hacks have been linked to a group called Deep Panda, which has ties to that country's government.

If a government is behind the attacks, it may not be looking for financial gains or even be interested in health care data, said Schmidt.

"However, they may care about some of the indirect side effects," he said.

For example, a government may indiscriminately collect data assuming that it will eventually find useful information. Governments could also use attacks against Western companies as training exercises to learn how IT systems work. Many businesses use the same technology so their IT infrastructures share similar setups.

"There's a lot of knowledge that's transferable from mucking around a big firm," he said.