I have this message on a Debian Etch 4.0: "Warning: This operating system is not fully supported!"
# rkhunter --version
Rootkit Hunter 1.2.9
Logged In: YES
Version 1.2.9 is no longer supported and distributions that have not upgraded to version 1.3.2 should have their security stance checked. Please upgrade to version 1.3.2 either from Debian package or source tarball. Thanks.