7thcircle

All of that info is great but I would add that you might consider restoring a known good version of your site since it is so hard to get everything they leave behind. You may also consider paying Sucuri to fix it because I believe they give you a year of their firewall with every fix.

This should fix it.

<?php
// Set Sender (Return Path) to From address
if ( ! function_exists( 'edl_setemailsender' ) ) {
	add_action('phpmailer_init', 'edl_setemailsender');
	function edl_setemailsender($params) {
		if(filter_var($params->Sender, FILTER_VALIDATE_EMAIL) !== true) {
			$params->Sender = $params->From;
		}
	}
}
?>

You can use custom questions, or create an option for each shirt size and a quantity for them.

I have never seen that popup on my installs. I also can not find anything about it in the control panel. Do you possibly have something setup to that effect in PayPal?

When you register, there should be a drop down to select the quantity of the registration item you created. Just choose more than one and it will ask for the extra names.

Excellent. Happy to help.