I've a one page checkout. When I click on 'continue' button after select the shipping method it redirects to dashboard page. I've noticed that it print a '499 request forbidden by antivirus' in the console, and I've noticed that this issue happens only in computers that have Kaspersky intalled. I can't give up all customers with Kaspersky installed. What to do? Thanks Guys.
Add your Magento site and all related domains (including files hosted elsewhere but included in your template) to the KAV trusted sites list.
See this link for help: http://support.kaspersky.com/5418 (Mostly applies to PURE and similar single-license versions of KAV. If you have Endpoint Security, you need to build a rule into your policy at the Administration Server level. I could walk you through this if you need help.)
Edit: It occurs to me just now that you may not be talking about users you can control, but random customers around the web. If that's the case, you need to contact Kaspersky about why your site is on their blacklist and how to get it removed. I typically start here: http://support.kaspersky.com/virlab/helpdesk.html