Who are your friends on Facebook? Are you sure? Thomas Ryan, co-founder of Provide Security, knows that you can’t always be certain. Why? Because he created the fictional Robin Sage, a cyber femme fatale, who quickly wormed her way into the confidence of national security professionals who should have known better. He conceived the experiment to expose weaknesses in the nation's defense and intelligence communities, but even he was surprised by its success. Robin Sage is just one of the fascinating and disturbing tricks of the online espionage trade that Ryan shared with SPY Historian Mark Stout. You may never friend anyone again…