Fully qualified domain name

A fully qualified domain name (FQDN), sometimes referred to as an absolute domain name, is a domain name that specifies its exact location in the tree hierarchy of the Domain Name System (DNS). It specifies all domain levels, including the top-level domain, relative to the root domain. A fully qualified domain name is distinguished by its unambiguity; it can only be interpreted one way.

For example, given a device with a local hostname myhost and a parent domain name example.com, the fully qualified domain name is myhost.example.com. The FQDN therefore uniquely identifies the device — while there may be many hosts in the world called myhost, there can only be one myhost.example.com.

In the DNS, and most notably, in DNS zone files, a FQDN is specified with a trailing dot, for example, "somehost.example.com.". The trailing dot denotes the root domain. Most DNS resolvers will process a domain name that contains a dot as being an FQDN[1] or add the final dot needed for the root of the DNS tree. Resolvers will process a domain name without a dot as unqualified and automatically append the system's default domain name and the final dot.
Some applications, such as web browsers will try to qualify the domain name part of a Uniform Resource Locator (URL) if the resolver cannot find the specified domain. Some applications, however, never use trailing dots to indicate absoluteness, because the underlying protocols require the use of FQDNs, such as e-mail

Domain name

A domain name is an identification label to define realms of administrative autonomy, authority, or control in the Internet, based on the Domain Name System (DNS).

Domain names are used in various networking contexts and application-specific naming and addressing purposes. A prominent example are the top-level Internet domains com, net and org.

Below these top-level domains (TLDs) in the DNS hierarchy are the second-level and third-level domain names that are open for reservation and registration by end-users that wish to connect local area networks to the Internet, run web sites, or create other publicly accessible Internet resources. The registration of these domain names is usually administered by domain name registrars who sell their services to the public.

Individual Internet host computers use domain names as host identifiers, or hostnames. Hostnames are the leaf labels in the domain name system usually without further subordinate domain name space. Hostnames appear as a component in Uniform Resource Locators (URLs) for Internet resources such as web sites (e.g., en.wikipedia.org).

Domain names are also used as simple identification labels to indicate ownership or control of a resource. Such examples are the realm identifiers used in the Session Initiation Protocol (SIP), the DomainKeys used to verify DNS domains in e-mail systems, and in many other Uniform Resource Identifiers (URIs).

An important purpose of domain names is to provide easily recognizable and memorizable names to numerically addressed Internet resources. This abstraction allows any resource (e.g., website) to be moved to a different physical location in the address topology of the network, globally or locally in an intranet. Such a move usually requires changing the IP address of a resource and the corresponding translation of this IP address to and from its domain name.

This article primarily discusses the registered domain names, the domain names registered by domain name registrars to the public. The Domain Name System article discusses the technical facilities and infrastructure of the domain name space and the hostname article deals with specific information about the use of domain names as identifiers of network hosts.

Antivirus Software

Antivirus software mainly prevent and remove computer viruses, including worms and trojan horses. Such programs may also detect and remove adware, spyware, and other forms of malware.

A variety of strategies are typically employed. Signatures involve searching for known malicious patterns in executable code. However, signatures can only be updated as viruses are created; users can be infected in the time it takes to create and distribute a signature. To counter such zero-day viruses, heuristics may be used to essentially guess if the file is truly malicious. Generic signatures look for known malicious code and use wild cards to identify variants of a single virus. An antivirus may also emulate a program in a sandbox, monitoring for malicious behavior. Success depends on striking a balance between false positive and false negatives. False positives can be as destructive as false negatives. In one case a faulty virus signature issued by Symantec mistakenly removed essential operating system files, leaving thousands of PCs unable to boot.

Antivirus software can have drawbacks. If it is of the type that scans continuously, antivirus software may cause a significant decline in computer performance, it may present computer users with a decision the user may not understand. Antivirus software generally works at the highly trusted kernel level of the operating system, creating a potential avenue of attack
The effectiveness of antivirus software is a contentious issue.

One study found that the detection success of major antivirus software dropped over a one-year period