Do "normal" users own other executables (in the /bin, /sbin, /usr/bin and /usr/sbin directories)? Sometimes you'll see executables owned by "bin" - this is normal. If a true "normal" user owns these files, chances are you've been
compromised!
Does anybody other than yourself know the root password? Have you noticed lots of failed ssh connections, etc? Check your logs (/var/log/messages) and see if anything naughty is going on. Good luck.
If you've been compromised, you're only real option is to restore trusted executables - whether this be from installation media/backups depends upon your disaster recovery procedures.
And all of this assumes that you actually
have been compromised. And remember, a great deal of compromises come from somebody
inside organisations
Cheers
ZB