This where the hackers may have gotten themselves into trouble. To be totally safe, a Chinese hacker would log out of the servers used for cyber-espionage (and allegedly sponsored by the Chinese military) before logging into a separate, more low-key VPN that he or she could use to access U.S.-based social media sites such as Facebook and Twitter.

Instead of following that procedure, according to Mandiant, some of the hackers got lazy. “The easiest way for them to log into Facebook and Twitter is directly from their attack infrastructure,” the company’s report explains. “Once noticed, this is an effective way to discover their real identities.” When the hacker uses the “attack” servers to log in to Twitter or Facebook, he or she unintentionally links the espionage servers with specific Facebook and Twitter accounts — in other words, with specific human beings.