Leap only infects Cocoa applications, and it does not infect applications owned by the system (including the apps that come pre-installed on a new machine), but only apps owned by the user who is currently logged in. Typically, that means apps that the current user has installed by drag-and-drop, rather than by Apple's installer system. When an infected app is launched, Leap tries to infect the four most recently used applications. If those four don't meet the above criteria, then no further infection takes place at that time.