No security system is perfect and it is always good to have some forms of intrusion
detection just incase somebody does get in you can be notified. Do not immediatly
get worried if in an email you get a positive, many of them are false and from
upgrades. I would first suggest running "rkhunter -c" from ssh and looking at
the errors. If it is a few bad binaries you should check to see what was updated
recently. If you have a rootkit detected you should start to worry because it
is very uncommon for a false positive on a rootkit or trojan.