small changes in some librairies

Hi,

I've noticed a strange problem ( is it one ? ) :

Sometimes a bit changes in some of my librairies files ( without any
intervention from me )

Using an md5 checksum program ( called l5 ), i get :

(-) /usr/lib/libslang.so.1.3.6//F 80993 100755 1 0/0 452519 37d42da5 3.c4B007KC7UjmbLxB40x.
(+) /usr/lib/libslang.so.1.3.6//F 80993 100755 1 0/0 452519 37d42da5 3dF9uA2KyYDx2kamrAPr86

these changes occur between between 3 and 4 o'clock in the morning 

and later a reversed change occurs (between 4 and 5 am )

(+) /usr/lib/libslang.so.1.3.6//F 80993 100755 1 0/0 452519 37d42da5 3.c4B007KC7UjmbLxB40x.
(-) /usr/lib/libslang.so.1.3.6//F 80993 100755 1 0/0 452519 37d42da5 3dF9uA2KyYDx2kamrAPr86

I compared this file with another one : just a bit have changed in it

my computer was not connected to internet and have some security
features... but is these changes could be an virus, trojan , or
disk/system  error ?
A similary change occurs in libstdc++.so on another machine ....
I use a linux kernel 2.2.13 with last ipvs and raid patches.

Any ideas ?

zas
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