A SOX audit is performed to verify compliance with Sarbanes-Oxley. It's a 2002 law that came about in the wake of the Enron scandal. The law contains 11 titles, or sections, ranging from additional corporate board responsibilities to criminal penalties for lack of compliance. Overall it requires organizations to show that they have security controls and that there policies match their actions. An IT audit is very similar and again looks at the policies and controls. It may also assess the risk to critical infrastructure. Control Objectives for Information and related Technology (COBIT) is one of the leading frameworks used to guide and IT audit. You can learn more about it by visiting the ISACA.org website.
This was first published in March 2006