In Digital Combat, U.S. Finds No Easy Deterrent

This article was reported by John Markoff, David E. Sanger and Thom Shanker, and written by Mr. Sanger.

WASHINGTON — On a Monday morning earlier this month, top Pentagon leaders gathered to simulate how they would respond to a sophisticated cyberattack aimed at paralyzing the nation’s power grids, its communications systems or its financial networks.

The results were dispiriting. The enemy had all the advantages: stealth, anonymity and unpredictability.