WASHINGTON, Aug 27 (Reuters) - A Chinese hacking group

exploited a software bug to compromise several internet

companies in the U.S. and abroad, a cybersecurity firm said on

Tuesday.

Researchers at the firm, Lumen Technologies ( LUMN ), said

in a blog post that the hackers took advantage of a previously

unknown vulnerability in Versa Director - a software platform

used to manage services for customers of Santa Clara,

California-based Versa Networks. It said four U.S. and one

non-U.S. victim had been identified. Lumen did not name the

victims and did not immediately respond to a request seeking

further details.

Versa Networks issued an advisory on Monday acknowledging

that the vulnerability had been exploited "in at least one known

instance" by an advanced group of hackers, and urged customers

to upgrade their software to fix the bug.

Lumen's blog post said that its researchers assessed with

"moderate confidence" that the hacking campaign was carried by

an alleged Chinese government-backed group nicknamed "Volt

Typhoon." The attacks happened as early as June 12, Lumen said.

The Chinese Embassy in Washington did not immediately

respond to a request seeking comment, although Beijing routinely

denies allegations of its involvement in cyberespionage. U.S.

officials did not immediately respond to a request for comment

but on Friday the U.S. Cybersecurity and Infrastructure Security

Agency added the Versa vulnerability to its list of "known

exploited vulnerabilities."

Brandon Wales, the recently departed executive director of

CISA, was quoted by the Washington Post on Tuesday saying that

China's hacking effort had "dramatically stepped up from where

it used to be."

Volt Typhoon has emerged as a group of particular concern to

U.S. cybersecurity officials. In April, FBI Director Christopher

Wray said China was developing the "ability to physically wreak

havoc" on U.S. critical infrastructure and that Volt Typhoon had

burrowed into numerous U.S. telecommunications, energy, water

and other critical services companies.