Once upon a time, Cameron Simpson <cs(a)cskk.id.au> said:
The UseDNS one is only slightly security - by disabling DNS lookup
of incoming clients we (a) speed things up, particularly on high
latency links and (b) stop leaking information about who is
connecting to use to upstream DNS servers (from the DNS query).
FYI: "UseDNS no" has been the default in OpenSSH for a while now.
--
Chris Adams <linux(a)cmadams.net>