Hackers invaded systems at one of America's big three credit reporting agencies, gaining access to private information belonging to 143 million people - nearly half of the US population, as well as some consumers in Canada and the UK.

Equifax discovered the breach on 29 July, which exposed sensitive information such as social security numbers, birthdays, addresses and in some instances, driver's license numbers, and credit card numbers.  Equifax is the agency many people use to guard against identity theft and one that businesses turn to when verifying a customer's identity.

Chairman and CEO Richard Smith apologized to "consumers and our business customers for the concern and frustration this causes".  He added, "This is clearly a disappointing event for our company, and one that strikes at the heart of who we are and what we do."

Equifax, an international credit reporting agency with a branch in Australia, did not explain why it took more than a month to disclose the breach which put the personal information of millions at risk.  At the moment, it's not believed that Australian customers were compromised in the breach.

The company also admits three executives quickly sold stock after the breach occurred but before it was revealed this week.  Chief Financial Officer John Gamble sold shares worth US$946,374;  Joseph Loughran, president of US information solutions, sold stock worth US$584,099; and Rodolfo Ploder, president of workforce solutions, sold US$250,458 of stock in early August.

Equifax says the trio had not yet been informed of the incident.