My first rkhunter scan of my Ubuntu 8.04 os produced the seven warnings listed below:

usr/bin/curl
usr/bin/size
usr/bin/strings
checking for passwd file changes
checking for group file changes
checking /dev for suspicious file types
checking for hidden files and directories

Do these seven warnings indicate the existence of foreign software in my Ubuntu os? I do not know what the fuctions of the curl, size, or strings files are but I am sure worried about password file changes, suspicious files, and hidden files and directories. Is there a way to find out just what is in my computer?

How do I even check to see if the firewall is up and running?