Coming from a person with no computer knowledge...well...very little...logically, your question being taken at face value, then A would be more secure in that, although being critically vunerable, it is not under attack, therefore, is more secure...because, at face value, you do not say it will be attacked, it's just vunerable...therefore secure.
That does seem to make cense, however I read some time ago, that during the Blitz of London during WW2 there was no cases of the flue or colds............The argument was that due to the stress of living in constant fear the bodies imune system went into overdrive. Perhaps the same is true of computer systems??????