you have to program the security bits after you program all the ROM data.
After you program the security bits youcant see your code even.
here below the code that i use for the protection


void chipprotect()
{
setbit(vpp);wait10us();
setbit(p26);setbit(p27);setbit(p36);setbit(p37);
progpulse2(); wait10ms();
clrbit(p36);clrbit(p37);
progpulse2(); wait10ms();
clrbit(p27);setbit(p36);
progpulse2();wait10ms();
clrbit(vpp);
printf("chip protected !! n");
}