I just bumped into this story when I was looking for some info.It seems that other than visual aspects like allowing remote access via system access,intruders can also use Terminal to do a lot of evils if they are on the same LAN. Would someone please let me know how can I get sure that I have not same problem?How can I get sure when I am connecting WLAN of workplace nobody can hack my computer and if they did by any chance(having password) how can I hinder the problem?How a MAC could have two syslog? And if there is problem how can I get rid of it?I am scared I might leave my Mac unattended sometimes.
"As long as your roommate has physical access to the Mac & knows what he is doing, there is no way to prevent him from hacking it"
Quite simply, every single common modern OS has ways for you to get into it - from konboot to changing the password, to single user mode. There's nearly no way to secure a system with physical access. You can reduce the risk by setting up a password to allow booting, and encrypting your filesystem with filevault. This will make a casual intrusion harder.
As for online access - disable anything you don't need, and set up key based authentication. If you need remote access to the system use only an ssh tunnel. Disallow root remote logins and allow only specific users to log in. I'd also suggest using an uncommon port for a little more obscurity.