Australian authorities are working with the US government as it pursues the perpetrators of what is being called the world's biggest ever money laundering scheme, after Westpac accounts holding $US36.9 million were named by US prosecutors.

According to prosecutors, a Costa Rican company called Liberty Reserve was at the centre of a $US6 billion ($6.3 billion) money laundering operation that spanned 17 countries, including Australia.

It is alleged tens of millions in proceeds of cybercrime including pornography, credit card fraud and identity theft were funnelled through shelf companies and banks around the world.

The indictment names three Westpac accounts held in the name of Technocash Ltd containing $US36.9 million in assets linked to the offences. It is demanding it be forfeited to the US government.

After authorities tried to seize Liberty's accounts in Costa Rica, the document says funds were shifted into ''more than two-dozen shell company accounts held in locations around the world, including Cyprus, Hong Kong, China, Morocco, Australia and Spain''. No other Australian banks are named.

It is understood US authorities made a formal request for Australian involvement, and the issue has been investigated by agencies including Austrac and the Federal Police. ''Australian authorities are liaising with US counterparts in relation to this matter,'' an Austrac spokesman said.

The indictment document included the Westpac accounts in a list of ''forfeitable property'' that was linked to the offences.

Westpac would not say if the funds had been frozen, but said it had been working with authorities.

''We have rigorous processes in place to combat money laundering and have been working closely with regulators and law enforcement agencies,'' a spokeswoman said.

Sydney-based Technocash said in a statement that it was appalled at the allegations against Liberty Reserve.

"Technocash is fully compliant with Australia’s robust anti money laundering and compliance regimes, including Austrac reporting," it said. "Technocash is pleased to have helped authorities with their investigations wherever possible."

According to Austrac's annual report, there has been a 230 per cent increase in the number of suspicious matters and transactions over the past five years.