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Whois is a service that allows retrieving information about the owners of Internet addresses (domains) and IP addresses. The English phrase "Who is" ("Who is this") means that you can get contact information relating to domains and IP addresses.
To get the stored information, you need to know the corresponding whois server depending on the domain. Unfortunately, the queries themselves are becoming more complex because of the new extensions for different countries and the new generic top-level domains.

Using Whois, the information about domain names and IP addresses can be loaded. You need to know the corresponding whois server. If you do not want to deal with technical details, you can also start the inquiry via the numerous providers of web-based domain lookup. In many operating systems the information can be retrieved via the command line by simply typing whois example.com.

The obtained details about top-level domain can differ. But in general, the information concerns the domain owner, administrative contact, technical contact, zone administrator and the name servers. Name servers translate the complex IP address into the easy to remember domain and domain extension.

The obtained information may, however, be used only in certain cases. For example, it is prohibited to send spam to the received email addresses. It is explicitly allowed to establish contact in case of technical issues, infringement of rights of third parties or other problems with the domain or IP address.

Possible use of Whois depends on the administrative authority. They and the top five managers of IP addresses in the world provide various ways of retrieval of public information about a domain or IP address.
The administration of Whois information lies with the respective registration authority, e.g. nic.at administers .at domains, the Internet Corporation for Assigned Names and Numbers (ICANN) administers all generic and new top-level domains, and the Regional Internet Registries administer IP addresses. As a result, different versions of Whois service are used. Basically, the information retrievable by means of Whois queries also differs. Each registration authority has put in place slightly different information management rules.

A Whois query can often be the only way to obtain data from the domain holder if there is no legal notice. This is very interesting in different situations. The service was designed to give third parties the possibility to directly address the right contact in case of problems. For example, if the content under a domain violates the rights of a third party, it is possible to contact the person in charge.
Another conceivable case is when the domain causes technical risk. The service is particularly important to all those whose rights are violated by the domain. In times of cyber-bullying, it is a ray of hope to many victims defamed on a website with no legal notice.

The first contact person for domains is always the domain owner stored in the Whois data. If they do not respond, there is also the opportunity to address the administrative contact, technical contact or zone administrator directly and inform them about the infringement. This way, it is ensured that the violations of rights or problems are promptly eliminated.
Various data is provided depending on the registration authority. For example, only the name and address are available by default for the .de domains. Thus, the first contact should usually be established by mail. Other registration authorities also store electronic contact data for top-level domains permitting a more rapid contact by phone, fax or email.