Question about variable in flash

1)I have seen a website use this code

<embed…<src=“myFlash.swf?url=http://yoursite.com/clip.flv
I don’t know how to create and use this kind of variable (?url=) in flash

2)I often send date (such as Score) from Flash to PHP and then insert it to mySql

Ex : _root.loadVariables("mkScore.php?name=" & name & "&score=" & score & "",POST)

But i am afraid that someone or “something” by someway may get my secret url “mkScore.php” and changes their score like that :

mkScore.php?name=kingGame&score=1000000000
So i added more variable that names is “passkey” and my url looks like that
_root.loadVariables(“mkScore.php?name=” & name & “&score=” & score & “&passkey=123456tototete”,POST)
And then i will check it’s value in PHP when flash send data
Is this the best way to secure sending data and deny user changing their score. Are there some ways???
:rabbit::p: