Dear Julie,
Sorry to hear about the crashing. Hopefully it's fixed now. I don't think it was related to the door noise you heard.
You don't need to worry about this worm.
For a start, if you're not running ichat, then it isn't running, there is nothing to disable. If you don't use ichat, you have no ichat buddies, so there is nowhere for this to come from.
It is not a virus as such. It is a worm - it's actually not much of a threat, and is not illustrative of any technical flaw in OS X. - It is important because it is clear that threats will emerge for OSX, but this threat is a case of "social engineering" - It takes a program, disguises it as something else, and relies on the user accepting it, downloading it, running it, using the administrator password and then executing it. In other words it tricks you into running it on your system and bypassing security.
A laboured analogy might be if someone dressed as a policeman came to your front door, asked for your chequebooks, cards and pin numbers and seeing the uniform you handed them over - it would not be an indication of problems with either the police or the bank.
So you do not have too much to worry about just yet.
As for the second virus - the bluetooth one, that was patched by Apple a year ago.
A couple of useful articles
http://news.softpedia.com/news/Second-OS-X-Virus-In-Just-Days-18455.shtml
http://news.softpedia.com/news/On-Ignorance-And-The-Matthew-Principle-18315.shtm l
There are some things you can do to protect yourself. I have never had a virus of any sort, ever, but then I've also never seen Anna Kournikova nude.
a) Never click on attachments in emails unless you know who they came from and what they are. If unsolicited, ask the sender if they sent them and what they are. Never run anything unless you know what it is and why you are doing it.
b) think about what it is, an image should not require installing.
c) A returned mail/undelivered attachment will never ask you to click for the message. Always go the source webpage, never click through.
d) go to system prefs, sharing and make sure the firewall is switched on. In the advanced tab in firewall, make sure that stealth mode is enabled.
e) Separate the administrator account from the one you use daily. ie - if you are the administrator, set up another user account just for adminstering and make yourself into a normal user.
f) Safari, Safri preferences - general - do NOT open safe files after downloading.
g) If really worried - you could download and install Clam XAV - it's an open source virus checker. At the least it will filter out windows viruses. You can get it from Version tracker - when you install it, it will ask if you want to install the virus checking engine - say yes.
You don't have to have it just yet, but if you want that extra reassurance it won't hurt. You can download it from www.versiontracker.com
h) System prefs - sharing - Turn Personal File Sharing off.
I hope that helps a bit. I know your recent experience may not predispose you to accepting my assurances blindly, which is not a bad thing, but all advice is given in good faith and I'm reasonably good at making sure I differentiate my knowledge from my assumptions. I'm sure the shutting door was not related directly to the problems you had.
Anyway, It's not as frightening as it may seem. OSX is still a pretty good system, and it is much harder to infect and damage than windows because of it's inherent settings, particularly because user accounts are much more restricted in what they can do as default, but you can never completely prevent people from being tricked into opening the door and inviting burglars into the house.
Sorry that's so long, I hope it helps a bit.
Cheers
