WHOIS query is widely used for querying databases that store the registered user's info for a domain name but is also used for a wider range of other information.

That depends on the type of domain name you registers. Most Top-Level Domain (TLD) name Registrars like co.za are privacy compliant and do not publicly expose the details of the registered owner of a domain, but not all are. Even if the registrar is compliant your details can still be requested in cases where for instance criminal or copyrighted infrindgments come into play.

Some domain registration companies might provide an optional product that protects your details in a whois search, but again it depends on the type of domain you register. In most cases, you do not need to opt-in for additional security to protect your private info. Do some homework before you register a domain to determine if you need additional security for your domain.