After an online attack on Anthem, by far the largest breach in the industry, security experts warned on Friday that more attacks on health care organizations were likely because of the high value of the data on the black market.

Anthem, one of the country’s largest health insurers, said the hackers did not appear to have stolen information about its customers’ medical claims. But medical identification numbers were taken, along with Social Security numbers, addresses and email addresses, which could be used for medical fraud.

According to a federal database, many much smaller attacks across the country have included both medical records and financial information.

Medical identity theft has become a booming business, according to security experts, who warn that other health care companies are likely to be targeted as a result of the hackers’ success in penetrating Anthem’s computer systems. Hackers often try one company to test their methods before moving on to others, and criminals are becoming increasingly creative in their use of medical information, experts say.