Right, but TierNolan is saying that if one private key is exposed all private keys and addresses in that wallet can be found, not just that one - it only requires one private key and the data from a watch only wallet... both of which I imagine have been on an online machine. It needs to be a new/fresh Armory wallet, not just a new address in the same wallet.
This is important if you don't want to risk your coins.
Exactly.
The risk is low but possible. The key point is that Armory generates private keys in a sequence. It uses the watch-only info and the previous private key to compute the next private key. Once you have 1 private key and the watch-only info, you can compute all the remaining private keys. (I am pretty sure earlier keys are safe)
An example would be if an altcoin was created that had a malware in the official wallet itself. You download the official wallet for the altcoin and install it.
It scans your computer for watch-only wallets and sends them to some server. It also sends any private keys that you import into the wallet. That allows the attacker to generate any later private keys.
[Edit]
Fair enough. The attacker needs the watching only wallet + 1 private key. If they can get the private key, then the watching only info could very easily be obtained too, since that is on the online computer.