I actually don't think that's terribly relevant. Deliberate attacks are qualitatively different from natural events. They're not independent, so naive statistic

I actually don't think that's terribly relevant. Deliberate attacks are qualitatively different from natural events. They're not independent, so naive statistical comparisons are misleading. In particular, deliberate attacks have a significant social component, where the success of one attack, especially one that is widely known, can lead to more being attempted. Attackers can adapt to your countermeasures. There also seem to be an increasing number of people willing to destroy critical bits of society. In short, past rates are not a guarantee of future risks. I expect infrastructure attacks to be a growing problem.