SAPMSYST is the program that is executed when we try to log-on to SAP system.
You cannot read the code for this program.
The code for this program is protected by SAP to prevent any changes to it.

1) I have read that the only solution to view the code is to make a Transport order and, at when SAP import, it un-compress the data, at this moment you could see the code
You go in SE01, create a transport order, enter manually the key  R3TR PROG SAPMSYST, save, release the OT. Then open your debug in the STMS when you ask SAP to make an import .

2) I have read on a few blogs saying that this program is protected when writing the ABAP Code with some string and this can be removed only during the transportation.
The source code is protected by a keyword  :   *@#@@[SAP]

3) ABAP source code is saved in table REPOSRC
Check Database View D010SINF SQLX field.
The source code is hidden when SQLX field is set to 'X'.