When creating multiple monsters in space invaders, collision detection help

1

Quick question sirs:

Consider the code below which creates a monster into the stage every 2 seconds, and you firing a bullet every time you click your mouse…

var monster:MovieClip;
var bullet:MovieClip;

var monsterMaker:Timer = new Timer (2000, 100);
monsterMaker.addEventListener(TimerEvent.TIMER, addMonster);
monsterMaker.start();

function addMonster(event:TimerEvent):void
{
monster = new Monster();
addChild(monster);
monster.x = Math.random()*stage.stageWidth;
monster.y=0;
}

stage.addEventListener(MouseEvent.MOUSE_DOWN, fireBullet);

function fireBullet(event:MouseEvent):void
{
bullet = new Bullet();
addChild(bullet);
bullet.x = this.mouseX;
bullet.y = this.mouseY;
}

the monster class has a code which makes the monster move downwards, the bullet class has a code which makes the monster move upward. Assume they work ok =)

Next thing i want to do is to add collision detection into the bullet and here i have a few questions:

1.) does each of the monsters have a different instance name? or are they all just “monster”'s? and if so…

2.) if i make a constructor for the Bullet class something like…

    var enemy:MovieClip;

    function Bullet(target:MovieClip)
    {
           enemy = target;
           this.addEventListener(Event.ENTER_FRAME, moveBullet);
    }
               
  //then in the Bullet class, i put a HitTestObject to detect collision...
         
    function moveBullet(event:Event):void
    {
            this.y -=20;
           if (this.hitTestObject(enemy)==true)

                  //*Inserts a Function That Will Destroy Enemy *
                  //(something like, this.parent.removeChild(enemy)?)
    }


    then, in the Main Time Line, everytime i fire a bullet:

function fireBullet(event:MouseEvent):void
{
bullet = new Bullet(monster);
addChild(bullet);
bullet.x = this.mouseX;
bullet.y = this.mouseY;
}

   here is my question: there seems to be an error in my logic if there are more than 1 monsters in the stage.. If my bullet hits any one of the monsters, the code will think it has hit all of the monsters and thus destroy all monsters in the stage... Is there some other way to correct this? How will it know which monster was hit by the bullet if each of my monsters are maybe identical to the code?