FireEye Inc., the U.S. network security company best known for fighting sophisticated Chinese hacking, said in a report released late Monday that breaches attributed to China-based groups had plunged by 90% in the past two years. The most dramatic drop came during last summer's run-up to the bilateral agreement, it added, as reported by Reuters.

FireEye and other security companies said that as the Chinese government-backed hackers dropped wholesale theft of U.S. intellectual property, they increased spying on political and military targets in other countries and regions, including Russia, the Middle East, Japan and South Korea.

Another security firm, CrowdStrike, has observed more Chinese state-supported hackers spying outside of the United States over the past year, company Vice President Adam Meyers said in an interview.

Targets include Russian and Ukrainian military targets, Indian political groups and the Mongolian mining industry, Meyers said.

Read alsoAnonymous hacktivists attack world's banks, London Stock ExchangeFireEye and CrowdStrike said they were confident that the attacks are being carried out either directly by the Chinese government or on its behalf by hired contractors.

Since late last year there has been a flurry of new espionage activity against Russian government agencies and technology firms, as well as other targets in India, Japan and South Korea, said Kurt Baumgartner, a researcher with Russian security software maker Kaspersky Lab.

He said those groups use tools and infrastructure that depend on Chinese-language characters.

Read alsoRussia possibly behind ISIS hacker attacksOne of those groups, known as Mirage or APT 15, appears to have ended a spree of attacks on the U.S. energy sector and is now focusing on government and diplomatic targets in Russia and former Soviet republics, Baumgartner said.