+The adnsresfilter utility uses `tsearch' from the C library (a la SVID
+and X/Open). If your C library doesn't have tsearch you will find
+that configure arranges for adnsresfilter not to be built. To rectify
+this, install a C library containing tsearch, such as the GNU C
+library. It is best if tsearch uses an automatically-balancing tree
+algorithm, like the glibc version does. Simple binary trees may
+perform badly.
+
+You will probably find that GNU Make is required.
+
+
+SECURITY AND PERFORMANCE - AN IMPORTANT NOTE
+
+adns is not a full-service resolver. It does no caching of responses
+at all, and has no defence against bad nameservers or fake packets
+which appear to come from your real nameservers. It relies on the
+full-service resolvers listed in resolv.conf to handle these tasks.
+
+For secure and reasonable operation you MUST run a full-service
+nameserver on the same system as your adns applications, or on the
+same local, fully trusted network. You MUST only list such
+nameservers in the adns configuration (eg resolv.conf).
+
+You MUST use a firewall or other means to block packets which appear
+to come from these nameservers, but which were actually sent by other,
+untrusted, entities.
+
+Furthermore, adns is not DNSSEC-aware in this version; it doesn't
+understand even how to ask a DNSSEC-aware nameserver to perform the
+DNSSEC cryptographic signature checking.