Robin Sage, according to her profiles on Facebook and other social-networking websites, was an attractive, flirtatious 25-year-old woman working as a "cyber threat analyst" at the U.S. Navy's Network Warfare Command. Within less than a month, she amassed nearly 300 social-network connections among security specialists, military personnel and staff at intelligence agencies and defense contractors....

But Robin Sage did not exist.

Her profile was a ruse set up by security consultant Thomas Ryan as part of an effort to expose weaknesses in the nation's defense and intelligence communities - what Mr. Ryan calls "an independent 'red team' exercise."