MrMelody55,
If there exists a virus within a midifile, the worst that can happen to your keyboard (Ketron) is that it won't be able to play the song(s).
The password feature currently exists on all X, SD and XD series:
UTILITTY -> PAGE2 -> PASSWORD (F4) [XD-series]
UTILITY -> PAGE3 -> PASSWORD (F6) [SD1 and X-series].
Thanks,
AJ (Just back from Summer NAMM).