brown_betty has some excellent
practical information and advice about how to protect your LJ (and webmail, and all other login-required services) from account hacking/hijacking.
If you're familiar with the plights of dorkorific/shoebox_project (not linking because still under attack - DO NOT GO THERE, DO NOT CLICK ANY LINKS THERE),
copperbadge and shenanigans related to recent
stop_plagiarism stuff, you'll probably already know why you should read this.