CLANDESTINE: Unit 61398 of the People's Liberation Army has been recruiting computer experts for at least a decade. Its apparent purpose became clear only when a U.S. Internet security firm accused it of conducting a massive hacking campaign against North American targets.

FROM THE SHADOWS: Hackers with the Chinese unit have been active for years, using online handles such as "UglyGorilla," Virginia-based firm Mandiant said Tuesday as the U.S. prepared to crack down on government-backed cyber espionage. The Mandiant report plus details collected by The Associated Press depict a highly specialized community of Internet warriors working from a blocky white building in Shanghai.

JOB FAIR: Unit 61398, alleged to be one of several hacking operations run by China's military, recruits directly from universities. It favors high computer expertise and English language skills. A notice dated 2003 on the Internet said the unit was seeking master's degree students from Zhejiang University's College of Computer Science and Technology. It even offered a scholarships.