Setting up USB Port to only charge - on a publicly available computer

I am placing a touch screen in a publically accessable semi monitored area. I wan to allow perople to charge their USB devices, but don't want them to be able to access them or be able to upload malicious software. I tired removing the data lines, so that only the charging lines were connected... and then plugged in my iPhone. After a little googling, I found this: MintyBoost - The mysteries...