Login system virker ikke ?

Hej jeg har et login system men det beskytter ikke.

på www.hhzeit.1go.dk/tagwall/admin.php skal man logge ind og det virker fint nok men man kan os bare gå ind på www.hhzeit.1go.dk/tagwall/admin_2.php uden at logge ind ?

Koderne er her:

admin.php:

<?
include("data.php");
if ($_GET['loggain'] == "yes") {
if (($_POST['user'] == "$login") && ($_POST['losen'] == "$pass")) {
$_SESSION['admin'] = "online";
header("Location: admin_2.php");
} else {
echo "Fejl i brugernavn eller kodeord";
}
}
?>
<head>
<link rel="stylesheet" href="style.css" type="text/css">
</head>
<form action="admin.php?loggain=yes" method="post">
<table width="157" border="0" cellspacing="0" cellpadding="0" height="38">
    <tr height="19">
        <td align="right" valign="top" width="84" height="19">Brugernavn:</td>
        <td align="left" valign="top" width="83" height="19"><input type="text" name="user" size="10"></td>
    </tr>
    <tr height="19">
        <td align="right" valign="top" width="84" height="19">Kodeord:</td>
        <td align="left" valign="top" width="83" height="19"><input type="password" name="losen" size="10"></td>
    </tr>
</table>
<input type="submit" value="Log ind"  border="0">
</form>
<br>
<a href="guestbook.php">Tilbage til tagwall.</a>


admin_2.php:

<?
include("data.php");

if ($_SESSION['admin'] = "online") {
$conn = mysql_connect("$dbhost", "$dbuser", "$dbpass");
$get = mysql_db_query($databas, "SELECT * FROM guestbook ORDER BY id DESC");
?>
<head>
<link rel="stylesheet" href="style.css" type="text/css">
</head>
<a href="guestbook.php">Tilbage til Tagwall.</a><br>
<font class="rubrik">Beskederne:</font><bR><bR><br>
<table width='400' border='0' cellspacing='0' cellpadding='0' height='10'>
<tr height='100%'>
<td align='left' valign='top' width='100%'>
<?
while ($guestbook = mysql_fetch_array ($get)) {
print "<font face='verdana' size='1'><b>Namn:</B> ";
print $guestbook["name"];
print "<br><B>Besked:</B> ";
print $guestbook["msg"];
print "<br><B>Svar:</B> ";
if ($guestbook["svar"] == "HH-Zeit.tk Tagwall 1.0") {
print "HH-Zeit.tk Tagwall 1.0";
} else {
print $guestbook["svar"];
}
print "<br><B>IP: </B>";
print $guestbook["ip"];
print "<br><br><B>skrevet d.:</B> ";
print $guestbook["date"];
print "<br><a href=\"deletegb.php?id=";
print $guestbook["id"];
print "\">Slet beskeden</a> - <a href=\"answergb.php?id=";
print $guestbook["id"];
print "\">Svar på beskeden</a>";
print "<br><hr width='100' align='left' color='black' size='1'>";
}
mysql_close($conn);
} else {
print "<font color=\"blue\">Du skal <a href='admin.php'>logge ind</a> </font>";
}
?>
</td></tr></table>

Sig hvis i vil se nogle andre filer.
Håber i kan hjælpe.