strange system mail : what does this mean ?

[Bernard <bdebreil@teaser.fr>]

Hi to everyone,

My system (Debian Sarge) was left running all night (usually I shut it 
down). In the morning, I noticed that a system mail had come :

*************************************
From root@localhost.localdomain Thu Dec 04 06:25:57 2008
Return-path: <root@localhost.localdomain>
Envelope-to: root@localhost.localdomain
Delivery-date: Thu, 04 Dec 2008 06:25:57 +0100
Received: from root by localhost.localdomain with local (Exim 4.50)
       id 1L86io-0001bU-Hi
       for root@localhost.localdomain; Thu, 04 Dec 2008 06:25:57 +0100
From: root@localhost.localdomain (Cron Daemon)
To: root@localhost.localdomain
Subject: Cron <root@debreil> test -x /usr/sbin/anacron || run-parts 
--report /et
c/cron.daily
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: 
<PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin>
X-Cron-Env: <HOME=/root>
X-Cron-Env: <LOGNAME=root>
Message-Id: <E1L86io-0001bU-Hi@localhost.localdomain>
Date: Thu, 04 Dec 2008 06:25:57 +0100
Status: RO

/etc/cron.daily/standard:
Files were found in lost+found directories. This is probably
the result of a crash or bad shutdown, or possibly of a disk
problem. These files may contain important information. You
should examine them, and move them out of lost+found or delete
them if they are not important.

The following files were found:


/boot/lost+found:
   #171379

************************

There is no possibility that my system may have shutdown : it wouldn't 
have restarted on its own. Besides, I have an APC system that is 
supposed to manage power failures, and, it this system had recorded any 
problem such as temporary power failure or voltage variation, it would 
have generated a special system mail. So, I wonder what the reason of 
the above system mail is. I tried to check what was that "#171379" file 
or whatever, in the /boot/lost+found directory. It appears to be a 
directory. Any direct trial to get into that directory fails :

/boot/lost+found#cd #171379
/#

So, I had to use the Midnight Commander, and I could see that the 
directory  '#171379' contained 10 files as follows :

device.map            30            19 aug 2007
e2fs_stage1_5    7776            19 aug 2007
fat_stage1_5      7504            19 aug 2007
jfs_stage1_5
menu.lst
menu.lst~
minix_stage1_5
reiserfs~tage1_5
stage1
xfs_stage1_5


Could anyone tell me why have such files ended up in this 
/boot/lost+found directory ?  Could this be the side result of a virus 
or other unfriendly attempt ?

Does this kind of warning call for any relevant test ?

Thanks in advance for any advice

Bernard