Verifying rkhunter file warnings
I got this problem as my rkhunter installation detected changed files (due to updates), so I encountered this solution by steve as I was searching for a solution.
Of course, as there could be a root kit/trojan/malicious stuff running in your system as rkhunter's meant to detect, you should NOT fully trust anything running from the machine. But I had to rely on this solution temporarily until I can get it (rebooted and) checked out proper using a tool like Finnix.
Am reposting the script here for reference, but you can get the most recent copy of the script here .
Getting your server to send an email whenever anyone logs in
Running on a VPS like Linode give me plenty of control over what is run, and also plenty of chances to learn more about network administration (along with the heartaches). 
The code that I used was based from this forum post. This one presumes that your MTA has been setup properly. The original code was for protecting your root account (i.e. when anyone logs into your server's root account, you get the notification).
(Note: it is usually not advisable to login as root. Create a user account and give it sudoer rights instead. I'd say that's advisable even for servers where there is only one person expected to login, which is you.)