Magento: ‘undefined’ pop-up alert on Place order at checkout after upgrade

‘undefined’ alert pop-up is shown after click on Place Order button at Magento checkout page after Magento upgrade: Cause Most likely cause is missing form_key attribute in the order form. Solution Check app/design/frontend/yourpackage/yourtheme/template/checkout/onepage/review.phtml and app/design/frontend/yourpackage/yourtheme/template/checkout/onepage/review/info.phtml files and replace the following code: with Do not forget to Flush Magento cache after the changes. If the issue persist, or form_keys are in place already, to troubleshoot the problem further edit skin/design/frontend/package/theme/js/opcheckout.js in your theme, search for alert(msg);… Read the rest