When Salesforce introduced Setup Audit Trail? Summer’11
Summer ’11 Force.com Platform Release
Set Up Audit Trail
Summer ’11 continues to improve Force.com’s audit trail tracking. The Set Up Audit Trail feature will track any changes made on behalf of another user. This capability is very important for tracking changes made by delegates or by support personnel. The audit trail will now reflect this additional information, ensuring that all your changes and processes are in compliance with most security policies.