(Bloomberg) — The FBI said it's close to finding the hackersresponsible for the attack on health-insurance company Anthem Inc.that exposed personal data on about 80 million customers.

Federal Bureau of Investigation officials are still decidingwhether to publicly reveal information about the attackers in oneof the biggest thefts of medical-related customer data in U.S.history, Robert Anderson, the bureau's executive assistant directorfor cybersecurity, said Tuesday.

Agency officials don't want to compromise investigations oroperations by any disclosures, he said.

"If you're going to be calling out nations or actor sets you'vegot to be willing to provide some of the technical findings,"Joseph Demarest, assistant director for the FBI's cybercrimedivision, said in Washington Tuesday. "Sometimes it's almostimpossible without giving up or compromising current ongoingefforts to understand those actors."

Investigators have found some evidence in the breach of SocialSecurity numbers and other personal information that points toChinese state-sponsored hackers, three people familiar with theprobe told Bloomberg News early in February.

Anderson said he didn't know yet whether the Chinese governmentcarried out the attack.

The FBI is tracking 60 hacking groups backed by foreigngovernments, the majority of which come from China, Demarest toldreporters. He also said that the Islamic State terrorist group inSyria and Iraq lacks the capability to carry out hacking attacks,although the FBI is concerned the group will acquire moresophisticated skills and tools.

Sony Hack

"In some of these cases you're going to be able to identifyactors much early on," Anderson said. It will take longer toidentify"the ones that are very sophisticated that can obfuscatetheir attack" by using different Internet protocol addresses aroundthe world.

In another case, the FBI and other U.S. agencies were able todetermine within weeks that the North Korean government attackedSony Pictures Entertainment. Anderson said there will be more caseslike Sony in which the attackers are publicly named.

"The Sony case is not going to be a one off," Anderson said."You're going to see us start to do this because, honestly, thecommunity and the guys and gals that are working cyber — both onthe law enforcement and national security side — are getting betterat it. You're going to see this more often."

Demarest also said the FBI would lose the ability to searchphone records for cybersecurity investigations if Congress doesn'trenew Section 215 of the USA Patriot Act, which expires June 1.