Security tips for NAS owners

I'm concerned about running software on my NAS that could expose my data to the outside world.

I have not exposed any additional ports on my router, nor really done much beyond the default settings.

Once I did notice what appeared to be someone pausing/playing my music.

I have since put a password on my LMS interface (which is a PITA in some contexts).

Any suggestions on what to check for and where, in terms of having a good setup?