Associated Press Photographer Rogelio Solis in Corinth and writers Emily Wagster Pettus in Jackson, Jay Reeves in Oxford and Eric Tucker in Washington contributed to this report.
"I am in the process of updating security policies and am also working with center CIOs on additional measures recommended by US-CERT to mitigate removable media risks, " wrote chief information officer Jonathan Pettus in an e-mail to employees.