The remote DNS server is vulnerable to a denial of service attack.
The remote host is running Bind, a popular name server. Versions of Bind 9.7.1-9.7.2-P3 are affected by a denial of service vulnerability. There is a small window of time after an authoritative server processes a successful IXFR transfer or a dynamic update during which the IXFR / update coupled with a query may cause a deadlock to occur. A server experiencing a high query and/or update rate will have a higher chance of being deadlocked.
Upgrade to BIND 9.7.3 or later.