From USENIX Security 2005!
without [secure deallocation], data can remain in memory for days or weeks, even persisting across reboots.
The span from first write to last read is the ideal lifetime. The data must exist in the system at least this long. The span from first write to deallocation is the secure deallocation lifetime. The span from first write to the first write of the next allocation is the natural lifetime. Because programs often rely on reallocation and overwrite to eliminate sensitive data, the natural lifetime is the expected data lifetime in systems without secure deallocation.
