One of the two hacker groups, which FireEye dubbed Tonto Team, is tied to China’s military and based out of the northeastern Chinese city of Shenyang, where North Korean hackers are also known to be active, said Mr. [John] Hultquist, a former senior U.S. intelligence analyst. FireEye believes the other, known as APT10, may be linked to other Chinese military or intelligence units.

The two hacking groups with alleged ties to Beijing have been joined by other so-called hacktivists--patriotic Chinese hackers acting independently of the government and using names like the "Panda Intelligence Bureau" and the "Denounce Lotte Group," Mr. Hultquist said.

South Korea’s Lotte Group has become a particular focus of Chinese ire after the conglomerate approved a land swap this year that allowed the government to deploy a Thaad battery on a company golf course.

Last month, just after the land swap was approved, a Lotte duty-free shopping website was crippled by a denial-of-service attack, said a company spokeswoman, who added that its Chinese website had been disrupted with a virus in February. She declined to comment on its source.