Iam running a website on Magento 184.108.40.206 and I've spotted that checkout pages of this website are being blocked by Kaspersky Internet security Software. This issue happened to myself and also was reported by several customers.
When going trough the checkout from Selecting delivery method to Payment method Iam kicked out by my Kaspersky Internet security with pop-up message "Dangerous URL blocked. and Iam redirected back to shopping cart unable to complete check out.
When I turn off Kaspersky Internet security I can check out OK.
The Kaspersky does not give much details in report, here is all I get: 26.01.2016 11.43.55;Dangerous URL blocked;https://www.domain.com/checkout/onepage/saveShippingMethod/;https://www.domain.com/checkout/onepage/saveShippingMethod/;Heuristic Analysis;Google Chrome;01/26/2016 11:43:55