How are $_SERVER variables sent from browser to server PHP
<p>I'm writing an app using php and have been looking into security issues. I'd like to know how the following code grabs browser information and how it is passed from the browser to the server:</p>

<pre><code>$_SERVER['HTTP_USER_AGENT']
$_SERVER['REMOTE_ADDR']
gethostbyaddr($_SERVER['REMOTE_ADDR'])
</code></pre>

<p>Is this information encrypted when it's passed from the client PC to the server? Would it be easy for a hacker to steal this data?</p>