The three state-owned Chinese companies at the centre of US cyber espionage claims have deep and long standing involvement in Australia, according to an American cyber security expert.

On Monday US attorney-general Eric Holder publicly indicted five Chinese soldiers on charges of stealing company secrets from American companies.

Washington claims that from 2006 five officers from a secretive hacking unit of the People's Liberation Army (PLA) called "Unit 61398" hacked the computers of US companies and stole secrets beneficial to three Chinese state-owned enterprises (SOEs) that were their direct competitors.

Dmitri Alperovitch is a former vice-president of threat research at security software company McAfee and has led two investigations into Chinese hacking and cyber-espionage against American companies.

The US did not name the three Chinese companies, only labelling them as SOE1, SOE2 and SOE3, but Mr Alperovitch told 7.30 it is clear from evidence in the indictment the companies are global aluminium giant Chinalco, Baosteel and nuclear company SNPT.

The three companies have long and deep connections with Australia.

"These are massive companies with billions of dollars in revenue and heavily involved in the world market," Mr Alperovitch said.

"Baosteel is in the acquisition stage of trying to acquire resources in an Australian company right now, so all these companies would be familiar to the Australian audiences because they're massive companies in China and they are very interested in resources and extracting resources from Australia and other countries."

He is referring to Baosteel's current attempt to takeover Australian iron and coal company, Aquila.

Baosteel has joint business interests with Andrew Forrest's Fortescue Mining and funds a research and development centre in Queensland involving four major east coast universities.

Chinalco was behind the failed 2009 merger with British-Australian miner Rio Tinto, while an ASX-listed wholly owned subsidiary of Chinalco, Yunnan Copper Resources, runs five mining projects in north Queensland.

SNPT buys vast amounts of Australian uranium and was involved in a 2011 takeover bid for a Perth company with large uranium holdings.

Mr Alperovitch is bound by confidentiality agreements regarding Australian companies that have been hacked, but says "they're major companies and they have lost significant intellectual property".

He says evidence indicates the company referred to in the indictment as SOE2 is Baosteel.

According to the indictment, a Unit 61398 officer created a secret database at SOE2 which was used to hold corporate intelligence about the iron and steel industries.

In early 2010, America's largest steel maker, US Steel, was embroiled in a legal dispute with Baosteel.

In the middle of the dispute, an email supposedly from US Steel's chief executive was sent to 20 of its senior employees.

It was actually sent by cyber hacker Sun Kai Liang, who used a technique known as spearfishing.

A link in the email downloaded intrusive malware onto US Steel computers, which enabled Wang Dong - operating under the pseudonym of UglyGorilla - to steal data from more than 1,700 US Steel computers.

Dmitri Alperovitch says the US Steel hack was typical of Unit 61398.

"We are seeing these patterns over and over again. We are seeing situations where companies are going into partnership with Chinese companies, or they have info that a Chinese company wants and we are seeing hacking attempts by the PLA to get that intellectual property and then that property ends up at these companies," he said.

"So it shouldn't be surprising if major manufacturing companies doing business in China are being hit by the PLA to benefit SOEs."