i was just thinking - can i get some nasty virus in my n770 while surfing web or checking e-mails?
it seems that nobody really is getting worried about it though...
how is it?

I don't even think virus scanning software exists for the 770.
I honestly wouldn't worry about it. Standard rules apply, don't run stuff you wouldn't trust, be aware of what you are downloading. It can't get a standard Windows virus, it would have to have been specifically developed for the Linux+ARM platform which is far less common and therefore not worth the work. It is probable that Opera has a flaw or two in it on the 770, but there really isn't the market base for someone to invest the time into finding a flaw, and exploiting it. That said, someone could write a proof of concept virus, but I wouldn't worry about it.

Besides, the slowdown of the device due to the scanner is far worse than having to reflash the device. And the latter is, as Het mentioned, highly unlikely.

Also, pretty much the only way to get you infected with something nasty is to install a deb. Now for those, it's really ridiculously easy to add something really nasty in them in addition to the software you were hoping to get. Anyway, I wouldn't worry about it. It's not like there would be much of incentive to write nasty software to the device as the market is still too small for it.