At least five multinational oil and gas companies suffered computer network intrusions from a persistent group of computer hackers based in China, according to a report released Wednesday night by a Silicon Valley computer security firm.

Computer security researchers at McAfee Inc. said the attacks, which were similar to but less sophisticated than a series of computer break-ins discovered in late 2009 by Google, appeared to be aimed at corporate espionage. Operating from what was a base apparently in Beijing, the intruders established control servers in the United States and Netherlands to break into computers in Kazakhstan, Taiwan, Greece and the United States, according to a report, “Global Energy Cyberattacks: ‘Night Dragon.’ ”

The focus of the intrusions was on oil and gas field production systems as well as financial documents related to field exploration and bidding for new oil and gas leases, according to the report. The attackers also stole information related to industrial control systems, the researchers noted, but no efforts to tamper with these systems were observed.

McAfee executives declined to name the victim companies, citing nondisclosure agreements it signed before being hired to patch the vulnerabilities revealed by the intrusions. Last year, when Google announced that intellectual property had been stolen by Chinese intruders, it expressed frustration that while it had observed break-ins at a variety of other United States companies, virtually none of the other companies were willing to acknowledge that they had been compromised.