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Using DNS to avoid malicious sites

by Chris Taylor

In the article "The Failure of Antivirus" (Ottawa PC News, November, 2011), I talked about how there is no such thing as a safe web site any more. As reported by the security company Sophos, in 2011, they found 19,000 new malicious URLs per day. Eighty percent of them were compromised, legitimate web sites.

There are frequent zero-day exploits for vulnerabilities in common software. A zero-day exploit is one for which no security patch yet exists.

The bad guys are reverse-engineering security patches to develop and distribute malware that exploits vulnerabilities before people get the security patches installed that fix those vulnerabilities.

Time frames to react are getting shorter and shorter. Signature file updates in antivirus software is simply not a complete solution any more. New techniques are needed to deal with all this bad stuff.

One technique that has been around for years and is now baked into browsers or available as a plug-in, is to verify the reputation of a web site before allowing your browser to render that content of a web site. Here is an example of how it all works.

Say you want to browse to The browser or a plug-in will first check the reputation of the web site through a trusted service. If it is not known to be bad, the browser or plug-in will allow the browser to load the page.

Let's say the reputation service gets word that the site has been compromised. They might find out through a report from a user. Or perhaps they have robots checking sites. As soon as they find out that a given site now contains malicious content, they can make a change in their reputation service so that the next time someone who uses their reputation service tries to go to the site, a code goes back to the browser to not load the page. Usually it will cause a warning page to be displayed indicating the site contains known malicious content. The user can then decide to over-ride the warning and go to the site anyway or they can heed the warning and avoid going to the site.

There was one part in the chain of events above that I skipped over.

Your browser has no idea about how to get to It can only go to an IP address, such as How does your computer figure out the IP address to go to? Enter DNS or the Domain Name System. You type in, your computer queries DNS to find the IP address and then your browser connects to the IP address.

What if you could combine DNS with a reputation service? That's exactly what Symantec has done with Norton DNS for Home. All you have to do is configure your DNS settings to point to Norton DNS for Home rather than the typical configuration where you point to the DNS server operated by your Internet Service Provider.

Once configured, all DNS queries go through the Norton DNS for Home server. If the site is not known to be bad, everything operates as usual. If the site is known to be bad, you get directed to a page that tells you why you are being prevented from reaching the site.

More than just malware protection

One of the cool things about Norton DNS for Home is that Symantec is actually running three DNS services. The first one blocks sites for security issues – malware, phishing, scam sites and web proxies. The second blocks based on security issues as well as pornography. The third blocks for security, pornography and what Symantec calls non-family-friendly sites that deal with mature content, abortion, alcohol, crime, cults, drugs, gambling, hate, sexual orientation, suicide, tobacco or violence.

If you have a router that you use to connect multiple computers to the Internet, Symantec recommends that you configure the DNS settings in the router to use Norton DNS for Home. If all computers connecting to the Internet through your router are set up in the default configuration, they will point to the router for DNS and automatically use Norton DNS for Home.


Setting a router to use Norton DNS for Home


If you only want certain computers to use Norton DNS for Home, you can easily configure individual computers to use Norton DNS for Home. Individual computer configuration is also good when you want to use different levels of protection for different computers. For example, you might have your own computer use protection just for security reasons. On the kids’ computer, you might go for protection for security, pornography and non-family friendly.


Setting DNS in Windows 7 to use Norton DNS for Home


Norton DNS for Home blocking access to a 'non-family-friendly' web site


While Norton DNS for Home is only for personal/home use, Symantec also runs a service for businesses.

To see how to configure your computer to use Norton DNS for Home, visit their site at

Originally published: May, 2012

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