function randomize(mnb) {
  mrnd= Math.floor(Math.random() * mnb)+1;
} 

document.write("Numéro: 4970 ");

for (i=1; i<=3; i++){ 
  for (j=1; j<=4; j++){ 
    randomize(9);
    document.write(mrnd);
  }
  document.write(" ");
}

document.write("<br />Expire &agrave; fin: ");

//md = new Date("December 5, 2001 18:15:00");
md = new Date();
mmonth = md.getMonth();
if(mmonth < 10) {
  mmyear = md.getYear()-100;
  mmonth+=3;
}
else {
  mmyear = md.getYear()-99;
  switch (mmonth) {
    case 10:
      mmonth=1;
      break;      
    case 11:
      mmonth=2;
      break;      
  }

}

if(mmonth < 10) {
  mmonth = "0"+mmonth; 
}
document.write(mmonth+"/"+mmyear);
document.write("<br />Code de s&eacute;curit&eacute;: ");

for (i=1; i<=3; i++){ 
  randomize(9);
  document.write(mrnd);

}