The remote host is missing an update to unbound announced via advisory DSA 1963-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201963-1

It was discovered that Unbound, a DNS resolver, does not properly check cryptographic signatures on NSEC3 records. As a result, zones signed with the NSEC3 variant of DNSSEC lose their cryptographic protection. (An attacker would still have to carry out an ordinary cache poisoning attack to add bad data to the cache.) The old stable distribution (etch) does not contain an unbound package. For the stable distribution (lenny), this problem has been fixed in version 1.0.2-1+lenny1. For the unstable distribution (sid) and the testing distribution (squeeze), this problem has been fixed in version 1.3.4-1. We recommend that you upgrade your unbound package.