And i suggest using Iceweasel via Easy Debian as mentioned before, cause opera is one f*** of annoying browser, not to mention closed source, so we can only guess if it's safe or not (ho ever i agree that it's probably safer than microB that wasn't updated in ages - but again, PROBABLY).

Also, i don't think You'll encounter many people prepared to attack microB, as N900 is (fortunately in this case) much less popular than android "kiddy" phones. Security through obscurity, that is Remember that even most talented "hackers" are as good in these situations, as "tools" they have with them. I don't suppose that anyone will write special script to hack you, even on Security Conference, just because hes annoyed that You got better handheld than her/his new 1k dolars one