Onepage Checkout – How to Fix Slow Onepage Checkout in Magento CE 1.9.0.1

I've implemented a multi page checkout on Magento previously and to be honest it proved to be more hassle than it was worth. I suppose it depends a lot on how much functionality the alternative checkout needs to modify (and if it uses any of the existing onepage checkout code). Personally I'd always be in favour of keeping the checkout as vanilla as possible as it keeps upgrades and maintaining modifications to a minimum. Checkout is arguably the most important part of the site so you need to make sure it is as robust as possible and for me sticking with the default onepage checkout is the preferred way of doing that.

I contacted Kaspersky and the issue was resolved. It was not a problem with Magento, just the URL of my domain was blacklisted.