Postgresql performed a "fast shutdown" by itself. Why? How was it able to do that? I've already googled and manual read as much as I could before posting this here.

Version info:  Postgres8.4 on Ubuntu10.x

I have a personal laptop that I run a postgres server on, and a Java script using JDBC was running for 1600~ mintues (that I have had running for weeks prior) before dying saying an administrator restarted the server.  Here is what I found in the pgsql logs:

Feb 29 07:46:55 krufe-laptop postgres[3578]: [2-1] 2012-02-29 07:46:55 EST LOG:  incomplete startup packet
Feb 29 07:46:56 krufe-laptop postgres[1113]: [2-1] 2012-02-29 07:46:56 EST LOG:  received fast shutdown request
Feb 29 07:46:56 krufe-laptop postgres[1113]: [3-1] 2012-02-29 07:46:56 EST LOG:  aborting any active transactions
Feb 29 07:46:56 krufe-laptop postgres[24095]: [2-1] 2012-02-29 07:46:56 EST FATAL:  terminating connection due to administrator command
Feb 29 07:46:56 krufe-laptop postgres[24095]: [2-2] 2012-02-29 07:46:56 EST STATEMENT:  SELECT high FROM onemin_interval WHERE ticker = 'QQQ' AND interval_end &lt;= 1329926940013 ORDER BY interval_start DESC LIMIT 46
Feb 29 07:46:56 krufe-laptop postgres[22214]: [2-1] 2012-02-29 07:46:56 EST FATAL:  terminating connection due to administrator command
Feb 29 07:46:56 krufe-laptop postgres[1252]: [2-1] 2012-02-29 07:46:56 EST LOG:  autovacuum launcher shutting down
Feb 29 07:46:56 krufe-laptop postgres[1250]: [1-1] 2012-02-29 07:46:56 EST LOG:  shutting down
Feb 29 07:46:56 krufe-laptop postgres[3582]: [4-1] 2012-02-29 07:46:56 EST FATAL:  the database system is shutting down
Feb 29 07:46:56 krufe-laptop postgres[3583]: [4-1] 2012-02-29 07:46:56 EST FATAL:  the database system is shutting down
Feb 29 07:46:56 krufe-laptop postgres[3584]: [4-1] 2012-02-29 07:46:56 EST FATAL:  the database system is shutting down
Feb 29 07:46:56 krufe-laptop postgres[3585]: [4-1] 2012-02-29 07:46:56 EST FATAL:  the database system is shutting down
Feb 29 07:46:56 krufe-laptop postgres[1250]: [2-1] 2012-02-29 07:46:56 EST LOG:  database system is shut down
Feb 29 07:47:10 krufe-laptop postgres[4318]: [1-1] 2012-02-29 07:47:10 EST LOG:  database system was shut down at 2012-02-29 07:46:56 EST
Feb 29 07:47:10 krufe-laptop postgres[4319]: [1-1] 2012-02-29 07:47:10 EST LOG:  incomplete startup packet
Feb 29 07:47:10 krufe-laptop postgres[4309]: [1-1] 2012-02-29 07:47:10 EST LOG:  database system is ready to accept connections
Feb 29 07:47:10 krufe-laptop postgres[4322]: [1-1] 2012-02-29 07:47:10 EST LOG:  autovacuum launcher started


I live by myself and noone else could ssh in from the outside to do this.  I was not home at the time this happened.  I viewed the auth logs for commands that were run during this time, nothing outside of normal cron commands.  Why would this happen?  What would cause this?  Can it be fixed/prevented?
If you have unattended security updates enabled, that would be a reason. A new version of postgreSQL (security update) was released today.