Types of corrosion on computers

[Sam O'nella]

I've seen rust and dust, but there's an old vaxstation II at Goodwill
Computers in Austin right now (very cheap, anyone welcome to buy it and get
it off my mind) but as most things, I checked out the back and see some
circles of white corrosion on the back where the cards? are contacting the
case.

I don't really have room or time but I don't own anything that uses QBUS or
is almost related to some of the neat iron some of you all collect (I've
mostly collected way too many home computer history items).

Anyway, what is that type of white corrosion on metal?  Would one probably
assume this means any bus would be corroded and this wouldn't be a computer
for the faint of heart hobbyist? I've only seen that maybe from batteries
but it's in an unusual place and pattern (I think).