There's various drive by attacks (when you visit a certain webpage, it can take advantage of an exploit say, with Flash, Java,
Doesn't concern me, noscript blocks all java & flash unless I specifically allow them.
or OS specific bug, to infect your system). Linux may be a little more immune in the sense that most of these type attacks target Microsoft and Apple systems mainly since Linux is not widely used to be a target, but that will change.
But that's not the only reason why linux is harder to target - no attack can do anything if I don't give it permissions, since my web browser doesn't run with root permissions it can't do anything to anything except to the files in my home directory. And I back up those regularly. And any OS bugs get quickly fixed on linux since it's open source and there's lots of people constantly working on the source code.
As for your older system, it probably doesn't support virtualization acceleration either so that pretty much limits you but trust me when I understand why folk keep older systems.
Yeah it's mainly about the money, by which I mean the money I don't have...
Anything that could happen in general really. EMP explosions, solar flares, and who knows maybe an asteroid.
I was watching a documentary the other day and scientists that watch the skies can not watch all of it.Most is still un observed.They said on the show that we could spot one coming and have only a month to kiss our selves and our arses good day. So kiss the kids and loved ones every day and show them your love because you just never know.
The entire universe could just end one day, there's no way of knowing... oh and we might all be brains in a box in a very elaborate computer simulation, there's no way of knowing that either...
Thing is, I'd rather not spend my time worrying about things that are unknowable - if things like that happen then they happen and that's that, it's not like any of us are going to be here forever anyway so it's best to just concentrate on living your life the best way possible in the time you have available. Living is no fun if you spend all of it worrying.