When you register a domain such as a .com or .net, your registration details are made publicly available by default. This is the standard for most domains.

ICANN, is the main center for domains and they set the standards for how this information should be dealt with. This is how ICANN describes WHOIS services

WHOIS services provide public access to data on registered domain names, which currently includes contact information for Registered Name Holders. The extent of registration data collected at the time of registration of a domain name, and the ways such data can be accessed, are specified in agreements established by ICANN for domain names registered in generic top-level domains (gTLDs). For example, ICANN requires accredited registrars to collect and provide free public access to the name of the registered domain name and its nameservers and registrar, the date the domain was created and when its registration expires, and the contact information for the Registered Name Holder, the technical contact, and the administrative contact.

However it is possible to protect your identity when registering certain domains. If enabled, this ID protection redirects anyone who is trying to find out who owns a domain to another website where they can send an email to the admin contact of the domain without knowing any of the specific details of the owner. This way the ICANN standard is met, but also your personal information is kept safe.

To take advantage of this feature, simply click the tick box that is labelled “Id Protect” when ordering a domain name. This service is free of charge.