Kaspersky False Positive in Magento 1.9 CE Onepage Checkout

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've played around with a horizontal checkout a while ago and you're free to use the code. It's on Github and except for a helper class it's all templating and some CSS. If you have specific issues or questions let me know, I'll try and explain.