If  you  press  Alt+F12  you can see the prompt "KEY" - Then type
"wlrnwhdakf"  or  "doomsday" and then you can see the words "Cheatcode
Enable".  Press  ALT  +F12 and then press Enter key to type one of the
cheat  codes below. * Every time before typing the cheat code you have
to press ALT + F12.

     1). onekill on/off : You can shoot the enemies down with one shot.

     2).  money "certain amount". You can make certain amount of money
from  1  to999 after you type "money" and the amount you want to have.
(example : money 300)

     3).  timer  on/off : If the mission has a time limit you can turn
the  timer  off  so  that  you  can complete the missions without time
limit.

     4).  invulnerable  on/off: After typing "invulnerable on" you can
upgrade the modes to God mode so that the character does not die.

     5). int 1~999: Change the character's intelligence quotient after
you  type  "int"  and  "any  number"  from1  to  999 that you want the
character to have. (example: int 144)

     6).  dex  1~999:  Change  the  speed of the move of the character
after  you  type  "dex" and any number from 1 to 999 that you want the
character to have. (example: dex 999)

     7). hit 1~999: Change the character's physical strength after you
type  "hit"  and  any  number  from 1 to 999 you want the character to
have. (example: hit 555)

     8). str 1~999: Change the character's muscular strength after you
type "str" and any number from 1 to 999 you want the character to have. 
(example : str 888)