If I were a global terrorist in the early 21st century, I would pay a lot of attention to the rampant insecurity of COTS installations at most web sites and ISPs. I would select my intended casualty audience and determine which type of damage (theft, threats, service outages, etc) would best terrorize that population. Then I would make a dynamic map of the C3I needs of that population, extended to include power, and find the most cost effective attack points. Perhaps that means exploiting poor RIP/BGP protocol interactions at the MAE level to disrupt North American Internet traffic during a televised protest, bombing Pamplona's power grid, or jamming AT&T switching equipment on Mother's Day.
The point is that a few Evil Geeks could do some really bad things to internet service if they were reasonably motivated and had attended the right party at DefCon. It seems likely that a terrorist organization willing to unleash Sarin on innocents would be quite interested in causing those bad things to happen.