Ok so I found it in the source, this line was manually added as per the instructions in the readme.html file that came with the security patch. What's the value that I need to enter?

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Open the file in an editor and find the function "zen_draw_form"

The last line of this function is

return $form;
Just before that line add another line as below

$form .= '<input type="hidden" name="securityToken" value="' . $_SESSION['securityToken'] . '" />';
You can then save the file.
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