"Files containing records of simulations carried out on the program were deleted Feb. 3," Malaysian police chief Khalid Abu said.
Read more:
Malaysia: Files Were Deleted From Flight Simulator - Business Insider
Of course, when you hit the "delete" key the file is not actually deleted; all that happens is the index entry pointing to the file segment locations on the hard drive is deleted and as long as that disc space is not subsequently overwritten, it should be possible to restore the file....so hopefully more details on the missing files will emerge.