[ubuntu-uk] Ubuntu (linux) vulnerabilty?? Comment please

[alan c]

With Ubuntu in mind I would be grateful for more information about the 
possible vulnerability - or not - of the sort of malware (trojan) 
which is likely to be used in the sort of current, and on a new scale, 
attack via infected websites as described in the Guardian:

http://www.guardian.co.uk/international/story/0,,2106855,00.html

My initial reaction is of course that linux doe snot install anything 
without a password, but then I remembered that in my user activities I 
was able to install a firefox extension without a password (I think), 
and in principle  I can install into my user area with no password 
generally.

So could a trojan be installed easily from an infected website without 
my knowledge?
-- 
alan cocks
Kubuntu user#10391