First off all we should start with your last question RedFox.
...I guess I was thinking about who would stand to gain by shutting down sott/sotts users
It almost never works this way. What i mean is , attacks on forum communities are launched mainly for one purpose - to get as much zombie computers - which would obviously involve infection. Zombies ( term used to describe computer infected by troyan or worm or both combined with virus ) are used later to send SPAM or to perform attack known as DDoS ( Distributed denial of service ) which is nowadays one of most profitable buisneses ( my spellchecker faild here :P ) on internet.
More zombies they get , better attacks they will have in future. Ill just mention that game aims to get literally 1000s or 10000s
of zombies.
Now to details of attack.
Very often hosting is company puts a lot of www sites of their clients on one or two PCs , if a hoster is big then they have whole farm of servers. Point is that those servers are connected via gigabit ethernet ( cheap and efficient ) which creates LAN at their side.Then this LAN is hidden behind firewall. Here we have to mention that firewall is never that kind of super dooper magic machine that kills all bad things flowing through it. Its regular machine with operating system which is also configured by man and also has flaws in security and even more it has to let traffic over 80 port of tcp to flow inside ( 80 port is http - our www ).
Now , if attacker breaks into ANY of those machines in LAN behind firewall , then he instantly gains access to rest of computers via LAN which means that he can freely launch MiTM attack ( in this case it is ARP poisoning because of ethernet like network).
ARP poisoning in ethernet is low-level attack which supports MAIN attack in switching envrioment - SNIFFING.
Sniffing goal is to capture all traffic between victim computers , in this case it will be firewall/gateway of hoster and webserver - both in LAN of hosting company. When attack is properly launched , attacker simply redirects all traffic to machine he already compromised ( probably other server in LAN ) which means he has total control over this traffic , he can manipulate it , inject malicious data inside streams , capture passwords , modify posts online - in short everything that flows through it.
Sott forum runs over http protocol which is plaintext , which also means that data going between webserver and firewall and in effect between sott forum user is not encrypted. Thats why it is strongly suggested to use https instead of http or at least authentication certificates ( yes i know , pain in ass to configure and to persuade users to use it ;P )
HTTPS is encrypted HTTP , so all attacker will get would look like for example like this:
!@#$#%^#$#GFSCFQ#RFAAweda34q34
instead of this :
username:drygol
password: my password :P
Problem that attacker have to face is fact that not all users use same software. For example , you just said that you got garbage on screen in one moment , this could mean that you have different browser that other targeted users , and exploit ( malicious software injected by attacker ) used by attacker didnt affect your PC - i could guess that u use firefox or opera and attack was launched against internet explorer ( most possible scenario nowadays ) . Or maybe you used Ie 7.0 and attack was launched against Ie 6.0. ( Dont write which browser you use here , even if i am right )
Ok now to after attack stuff.
If hosting company says TRUTH that it was arp poisoning attack , then it would mean that attacker is quite skilled , its not an easy stuff to break in , gather enough information about network and launch succesfull mitm. I tell you not easy. So we could exclude script kiddies here. So if that was skilled guy then he most probably have access to 0-day exploits.
0-day is that one you just mentioned - unrecognizable by virus or anti-spyware/malware software.
Also attack could be performed ( easiest way ) by someone who already has access to LAN , some one who could attack from inside.
And finally we have to reconsider possibilty that this attack was specially constructed in this way , to look like it was attack aimed to get as much zombies as possible , and in the same time its purpose was totally different - hint: gov ;)
I tried my best to construct sentences for regular reader but i can imagine that it can be hard to understand , also my engrish is faulty here :)
If you have more questions , go ahead , shoot.