Predictable and not going away
The ridiculous security infrastructure in place along with holes deliberately punched through by agencies like the NSA make this not just likely, but inevitable. Sony will not be the last to witness such a breach.
If you have not had a visible breach of any kind and you have a valuable network I would not be too smug that I had a secure system. I would be suspicious that you have already been penetrated if you have never seen any visible sign of a partial breech. The really dangerous malware seals up your system so other malware (or legitimate attempts to reclaim the system) cannot break its grip.
You are not going to see a zero day exploit on your system if it has already been used, your system captured and the weakness fixed by the intruder.
By their nature at least some zero-day exploits are very hard to anticipate. In most cases, your just hoping that you get notice and a fix before a breech because some other sucker took the hit.
Mortals attempting to keep complex heterogeneous systems secure don't have much of a chance against strong attacks.
Having said the above, a down and dirty way for medium to large companies to at least make net facing systems less attractive as targets is to just get someone who knows what they are doing to make sure that hardware firewalls seal the perimeter.
Biting the hand that feeds IT
