Change in suid root files

From: Robert (robert_schmidli@hotmail.com)
Date: 04/02/03 

From: "Robert" <robert_schmidli@hotmail.com>
Date: Wed, 2 Apr 2003 21:19:39 +1000

I am running Mandrake 9.0 on a permanent internet connection. I have msec
running (level 3). I frequently get the following messages.

Security Warning: Change in Suid Root files found :
                - No longer present suid root file : /bin/mount
                - No longer present suid root file : /bin/ping
                - No longer present suid root file : /bin/su
                - No longer present suid root file : /bin/umount
                - No longer present suid root file : /sbin/pwdb_chkpwd
                - No longer present suid root file : /sbin/unix_chkpwd
                - No longer present suid root file : /usr/X11R6/bin/Xwrapper
                - No longer present suid root file : /usr/bin/at
                - No longer present suid root file : /usr/bin/cdrecord
 [more follows]

What is the likely cause of this? I run chkrootkit regularly and it doesn't
pick up any evidence of an intrusion. Could something else be running that
is changing the file properties?

Could someone direct me to a url that explains what suids are all about?