The Domain Name System (DNS) acts as an address book for the internet by translating website names into their numeric equivalents that are used to locate the servers on which sites are based.
DNS filtering refers to a technique that is used to block access to known malicious or harmful sites. When a site, or group of sites, is identified as a threat the IP address that is used to find it is blocked using a filter and thereby blocks the site from access. Examples of sites that may be targeted in this way include malware sites, phishing sites, gambling sites or others that have been identified as posing a significant security risk to users. This technique is used by businesses to limit the potential threats that they are exposed to and help to reduce the workload of dealing with remediation activities that are required to deal with suspect sites as well as improving employee productivity.