The incident happened for two reasons: The contractor forgot to encrypt the email and the software in place to catch such errors did not work properly.

The Los Angeles Times reports that about 4,000 Securities and Exchange Commission employees may be at risk after their Social Security numbers and other payroll information were included in an unencrypted email.

The email was sent out May 4 by a contractor at the department's National Business Center. Drew Malcomb, a Department of Interior spokesman, says the incident happened for two reasons: The contractor forgot to encrypt the email and the software in place to catch such errors did not work properly.

Malcomb says there is no indication that the data was accessed. The agency has launched an investigation, which will likely result in a change of software.