Complex sentence: Some Internet service-providers rewrite the NXDOMAIN (domain does not exist) responses from DNS servers, which forces web browsers to a search page whenever a user attempts to browse to a domain that does not exist.
Split into simpler sentences: Some Internet service-providers rewrite the NXDOMAIN (domain does not exist) responses from DNS servers. This forces web browsers to a search page whenever a user attempts to browse to a domain that does not exist.