function createRandomPassword(hashLen:uint, includeLowercase:Boolean = true, includeNumbers:Boolean = true, includeUppercase:Boolean = false):String {
	var strHash:String = "";
	if (includeLowercase) strHash += "abchefghjkmnpqrstuvwxyz";
	if (includeNumbers) strHash += "0123456789";
	if (includeUppercase) strHash += "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	var maskPick:Number;
	var passwordStr:String = "";
	var maskLen:uint = strHash.length;
	for (var i:uint = 0; i < hashLen; i++) {
		maskPick = Math.floor(Math.random() * maskLen);
		passwordStr += strHash.charAt(maskPick);
	}
	return passwordStr;
}

trace(createRandomPassword(8));
// Output
// 6k3x10h8j

trace(createRandomPassword(6, true, true, true));
// Output
// D2jHEfT

trace(createRandomPassword(16, false, true, true));
// Output
// O8I2DTSLHHWRI50Z

trace(createRandomPassword(16, true, false, false));
// Output
// xxfeyshhqkrsqvhjt

trace(createRandomPassword(16, false, false, true));
// Output
// XMXIDTIXMNGNUXZT

trace(createRandomPassword(16, false, true, false));
// Output
// 4026352375069424

Based upon this (https://gist.github.com/988479) but made a few fixes.

AS3 Create Random Password

ActionScript 3