Starting in Mac OS X 10.7 (Lion), users can specify certain applications to be re-opened when a user reboots their machine. While this is usually done via a Graphical User Interface (GUI) on an app-by-app basis, there are property list files (plist) that contain this information as well located at
An adversary can modify one of these files directly to include a link to their malicious executable to provide a persistence mechanism each time the user reboots their machine1.
Holding the Shift key while logging in prevents apps from opening automatically2. This feature can be disabled entirely with the following terminal command:
defaults write -g ApplePersistence -bool no.
Monitoring the specific plist files associated with reopening applications can indicate when an application has registered itself to be reopened.