Whitney Houston's Final Movie -- Preemptive Strike to Prevent Leak

Whitney Houston's final movie is on lockdown ... over fears that people will leak Whitney's scenes and music ... TMZ has learned.

Sources connected to the production tell us ... the people working on "Sparkle" -- starring Whitney and Jordin Sparks -- are working "around the clock" to finish post-production work on the movie as quickly as possible.

We're told the building where the film is being edited is also under tight watch -- with ramped up security in the hopes of preemptively clogging a leak.

So far, no comment from Sony.