I'm concerned with the security implications of using a pool of unknown
time servers per default. If I understand correctly, anyone can
volunteer to participate in the pool. If the end user's ntpd is started
with the -g option, overriding the 1000 seconds sanity check (as was the
default in Ubuntu 7.10), and the server selects only one time server
from the pool to synchronize from, an attacker who controls a single
server in the pool can set the time of many Ubuntu hosts over the world.
Also, he will know the IP addresses of the victims. If any of them
happen to be interesting targets for the attacker, he can then mount
further attacks on all cryptographic protocols that depend on correct
time-keeping (for example, to prevent replay attacks). That would be a
serious security threat for the users.

-- 
default ntp.conf should use pool.ntp.org servers
https://bugs.launchpad.net/bugs/104525
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