WASHINGTON — A secret legal review on the use of America’s growing arsenal of cyberweapons has concluded that President Obama has the broad power to order a pre-emptive strike if the United States detects credible evidence of a major digital attack looming from abroad, according to officials involved in the review.

[link to www.nytimes.com]

The article says these powers were granted for overseas attacks, but that's what they said about drones too.