Shared Registration System
At one time, Network Solutions had a total monopoly on domain registration. As of 1999 the registration system was opened to allow multiple registrars to take part in the registration of domain names. This is called the Shared Registration System or SRS.
At present time, the registrars participate jointly in the maintenance of the SRS database. The SRS is still accessible through the whois tool but the information retreived from the SRS will only indicate who the registrar is instead of delivering the registered owner's information.
To get information, you now perform two whois lookups. One to the SRS and one to the registrar with whom the owner registered the domain.