Published: Oct 31, 2012 1:39 PM EDT
Updated: Nov 01, 2012 6:31 AM EDT

CHARLESTON, S.C. (AP) - About 3.6 million tax returns from as far back as 1998 were hacked in South Carolina in what experts say is the largest cyber-attack against a state tax agency in the nation.

Paul Stephens of the Privacy Rights Clearinghouse in California says there have been larger attacks against both private companies and the federal government that revealed information that could lead to identity fraud.

State officials say the attack was mounted from a computer with an international IP address. They say the attack was found earlier this month but they have not given many details because of the ongoing investigation.

The Revenue Department says Social Security numbers, credit card information and information from businesses may have been compromised in the attack.