The only thing you can do to keep your account safe is to pick a good password. Never use the same password in more than one place, don't pick one that is easily guessed by anyone who knows anything about you, don't use words that can be found in a dictionary as password. And, of course, don't tell anyone else your password, or write it down some place where someone can see it. :)
As for tracking, the forum only logs the IP address for posts and such activities, not for logins. There is another member who has also been posting with the same IP address as you, though that doesn't necessarily mean more than that you are using the same ISP to connect to the Internet.
Are any of these posts by you not actually by you? :)
http://www.lucasforums.com/showthread.php?p=2476054#post2476054)
http://www.lucasforums.com/showthread.php?p=2476091#post2476091)
http://www.lucasforums.com/showthread.php?p=2476119#post2476119)
http://www.lucasforums.com/showthread.php?p=2476537#post2476537)
How did you notice that your account had been used by someone else, by the way?
No; None of the posts were by me. In fact, my last official post (besides this thread) was in the Photo Album.
I noticed my account was hacked by looking at some PMs in my Inbox & Outbox, btw.