During financial years 2012-13 to 2014-15, Commonwealth entities detected or were informed of 4,828 incidents of internal fraud alleged against public servants or contractors, with losses totalling $11.3m. Each entity that experienced internal fraud was asked to select the one most costly incident each year and to provide information on the nature of the incident, the type of person who was alleged to have perpetrated it and how the matter was dealt with. The majority of the 126 incidents examined related to abuse of employee entitlements or financial benefits, with most committed through the misuse of information or documents, or other technology-enabled means. The findings show where risks of serious fraud against the Commonwealth lie and provide insight into how fraud prevention resources could most effectively be targeted.