The breach is the third time in two years USC has experienced a major breach of security on its computer system, The State newspaper reported.
The breach was discovered in January on a computer server at USC Sumter, but potentially affected people throughout the school's eight campuses because the information was on a shared server.
"Letters went out as soon as individuals were identified," USC spokeswoman Margaret Lamb said Friday. "There is no evidence that anyone's personal information was compromised or used improperly. USC Sumter has addressed the matter, notified the individuals and provided them guidance on how to protect their information."
USC Sumter didn't mail the letters until March 1, several weeks after the breach was found. The letters told those who might be affected how to check credit records.
"We've done everything we can do to address the matter," William T. Hogue, USC's vice president for information technology, said Friday in an e-mail.
The letter suggested those whose information was breached place an initial fraud report on their credit files and provided information on how to contact the three major credit bureaus.
The breach was caused by human error, but the school didn't provide further details or say who made the error.