In Iran, surveillance drones have kept an eye on nuclear activities while a computer attack reportedly has infected its nuclear enrichment facilities with a virus, possibly delaying the day when the U.S. or Israel might feel compelled to drop real bombs on Iran and risk a wider war in the Middle East.

The high-tech warfare allows Obama to target what the administration sees as the greatest threats to U.S. security, without the cost and liabilities of sending a swarm of ground troops to capture territory; some of them almost certainly would come home maimed or dead.

But it also raises questions about accountability and the implications for international norms regarding the use of force outside of traditional armed conflict. The White House took an incremental step Friday toward greater openness about the basic dimensions of its shadowy wars by telling Congress for the first time that the U.S. military has been launching lethal attacks on terrorist targets in Somalia and Yemen. It did not mention drones, and its admission did not apply to CIA operations.