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While registering new domain, the ICANN ( Internet Corporation for Assigned Names and Numbers ) ask you to provide personal contact information to update WHOIS information to set the identity of your domain. Once you fill the contact information then your listing will be available publically to anyone who choose to check information of your domain using Whois Domain checker tool.
There are lots of third parties available who may check your domain name in the WHOIS database.
Individuals, Registrars and Authorities can check domain details for expiration dats, transferring ownership and to investigate criminal activities based on their needs.