Computers at the South Carolina Department of Revenue have been attacked by a foreign hacker, exposing about 3.6 million taxpayer Social Security numbers.

About 387,000 credit and debit card numbers also were exposed.

Not all taxpayers’ information was affected by the computer server breech, said Gov. Nikki Haley during a 1:45 pm press conference at SLED headquarters Friday afternoon that included federal officials from the Secret Service and the IRS.

Officials asked anyone who has filed a state tax return since 1998 to visit protectmyid.com/scdor or call 1-866-578-5422 to determine if their information is affected. The state will provide those affected with one year of credit monitoring and identify-theft protection, officials said.

Pretty quickly, however, the phone line produced a busy signal. By 3:30, an auotmated response said people were encouraged to call at a later date due to the high volume of calls.

Mike Williams, the director of the Secret Service in South Carolina, said the breech is one of the largest the agency has seen but not the largest. His agency alerted state officials to the problem, he said.

State officials said they learned of the breech Oct. 10, put surveillance tools into place and shut down the hacker’s access Oct. 20. The offense is believed to date to Aug. 27, 2012, officials said; data was first taken in mid-September.

When asked who the hacker was and what steps officials are taking to find him, Haley said, “My instructions to them were to slam him to the wall.”

State officials and a private company are still looking to see if there are holes in the computer system, according to Department of Revenue Director James F. Etter.

Haley signed an executive order for an electronic security review at all state agencies.

Read more on this story in Saturday’s State newspaper.