[api]

In practice I would say Apple =~ Linux < Windows, though the latter can certainly be locked down if you know what you're doing.

However I think Linux's security is partly an artifact of a more techie user base. For a non-technical or too busy to be technical user I would say Apple offers the best security out of the box.

[fortran77]

A file that sitting on Windows that's been encrypted with a piece of well-audited encryption software is pretty safe. And if you want to be really certain, don't keep the machine connected to the internet except for software updates, and never while you're accessing your encrypted BTC archive.