FreeBSD Security Advisory (FreeBSD-SA-09:11.ntpd.asc)

The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-09:11.ntpd.asc
Upgrade your system to the appropriate stable release or security branch dated after the correction date
The ntpd(8) daemon is an implementation of the Network Time Protocol (NTP) used to synchronize the time of a computer system to a reference time source. Autokey is a security model for authenticating Network Time Protocol (NTP) servers to clients, using public key cryptography. The ntpd(8) daemon is prone to a stack-based buffer-overflow when it is configured to use the 'autokey' security model.