COLUMBIA, S.C. (AP) - State senators are investigating a massive tax breach at South Carolina's tax collection agency that exposed the unencrypted data of 3.8 million individual filers and 700,000 businesses.

A Senate oversight panel created earlier this month will hold its first meeting Wednesday morning.

The four-member panel will hear from officials with Mandiant, the computer security firm hired by the Revenue Department to determine what information was taken and how. The Virginia-based firm was hired Oct. 12, two days after the Secret Service notified state officials a breach had occurred.

Gov. Nikki Haley could not say with certainty how many people were impacted before she received Mandiant's report last week.

Panel co-chairman Kevin Bryant of Anderson says the subcommittee's job is to find out who's responsible for the agency's lax computer security.

For more on the hack attack, click here.