"Destructive cyber-attacks against critical infrastructure are coming." This was Gen. Keith Alexander's warning to the Aspen Security Forum last week. Gen. Alexander heads the National Security Agency and the U.S. Cyber Command. He should know what he's talking about--although he also clearly knows how to grow a budget.
According to Gen. Alexander, efforts to hack into U.S. infrastructure systems increased 17-fold between 2009 and 2011. However, the number of attacks for any given year were not provided.
A video of the interview with Gen. Alexander, conducted by NBC News correspondent Pete Williams, is available here.