The post One Exploit Should Not Ruin Your Day by Dino Dai Zovi made me think:
Finally, the larger problem is that it only took one exploit to compromise these organizations. One exploit should never ruin you day. [sic]
No, that is wrong. The larger problem is not that it "only took one exploit to compromise these organizations." I see this mindset in many shops who aren't defending enterprises on a daily basis. This point of view incorrectly focuses on exploitation as a point-in-time, "skirmish" event, disconnected from the larger battle or the ultimate campaign.
The real "larger problem" is that the exploit is only part of a campaign, where the intruder never gives up. In other words, comprehensive threat removal is the problem. There is no "cleaning," or "disinfecting," or "recovery" at the battle or campaign level. You might restore individual assets to a semi-trustworthy state, but the advanced persistent threat only cares that they can maintain long-term access to the environment.
If the problem were simply defending against a compromised asset, we would not still be talking about this issue. Rather, the problem is that it is exceptionally difficult, if not impossible, to remove this threat. Individual exploits add to the problem but they are only skirmishes.