I like to start this old topic again because I can't figure out what the problem is.
Every hour at xx:53 there's a mail to root like this:
Subject: [rkhunter] Warnings found for host@domain
Please inspect this machine, because it can be infected
I can't find any cron job that could cause this so the only way to reproduce this is, I guess, with the command #rkhunter -c --createlogfile, but I can't see any errors in the logfile.