The United States’ second-largest health insurer has been hacked.

Health insurance company Anthem has contacted its clients to tell them their records may have been stolen.

It means that the birth dates, medical IDs, tax file numbers, home addresses, emails and job histories of up to 80 million Americans could be in anyone’s hands.

Anthem Insurance CEO Joseph Swedish issued an apology statement say that even his personal info may have been taken.

Reports claim that the insurance company has now advertised for an encryption specialist.

Tech security expert Mark Bower has told the ABC that this style of digital theft is “inevitable in the industry landscape that we work in today”.

“Your information is being processed by enterprises, it's being shared by business partners, it's driving analytic decisions. And so data is pervasively used across very large sophisticated value chains, if you will.

“It's not just locked inside a database inside an organisation and we've seen that the attacks... are now using very advanced tools to bypass those traditional perimeter defences.”

The hack was revealed on the same day that Sony Pictures' CEO stepped down in the wake of a similar attack, and just a week before US president Barack Obama hosts a cyber security summit.