Bill Shorten has accused Malcolm Turnbull of "using Senator Sinodinos' defence" over the Parakeelia scandal, claiming it was "inconceivable" that Mr Turnbull, as Liberal Party treasurer, did not know about profits from the controversial software firm.

Mr Shorten sharpened his attack on questions about the Liberal party's relationship to a software company that it owns, Parakeelia Pty Ltd.

Liberal MPs pay the company $2500 a year in taxpayer allowances for use of its voter-monitoring software. Parakeelia in turn has transferred large amounts, exceeding $1 million over three years, into party accounts, giving rise to accusations the party is profiteering from public money.

Mr Shorten said it was "inconceivable" that Mr Turnbull, who businessman Ron Walker says was slated to succeed him in the company and as Liberal Party Treasurer in 2002, didn't know the arrangements between the party and the software firm.

"Now Mr Turnbull became the treasurer of the Liberal Party. It is inconceivable that when you are the national treasurer of the Liberal Party but somehow you don't know anything about this as far back as 2002? It is inconceivable," Mr Shorten said.

"How on Earth can the Treasurer of the Liberal Party be banking profits from a company that the Liberal Party owns … and you don't know what's going on?

"It sounds like Prime Minister Turnbull is using Senator Sinodinos's defence: 'I may have been the treasurer, I just didn't know what was going on'."

Senator Arthur Sinodinos told the Independent Commission Against Corruption in 2014 that he didn't know how much the firm Australian Water Holdings had donated to the Liberal Party at a time when he was both a director of the company and the party's treasurer.

Mr Turnbull has consistently brushed aside questions about Parakeelia, saying it is a matter for party officials.

On Friday, Ron Walker released correspondence confirming he had asked the Liberal Party's most senior official to remove him from company books a decade ago, despite continuing to be listed as a majority shareholder this week.

Mr Walker maintains that his role as Parakeelia's 98 per cent shareholder should have been assumed by Malcolm Turnbull, who succeeded him as federal Liberal treasurer and his role in Liberal companies in 2002.

"He succeeded me as federal treasurer of the party," Mr Walker said. "He assumed all responsibilities I had on that day."

The shares are non-beneficial and held in trust for the party.

But Mr Walker was forced to ask party director Brian Loughnane to take him off the company's books again, in 2007, when Fairfax revealed that he remained a shareholder despite promising to divest himself of political affiliations when joining the John Fairfax board.

"Please accept my resignation," he wrote in an April 2007 letter to Mr Loughnane. Party officials attributed his continued involvement to an oversight.

But party officials earlier this week said only that Mr Walker "believed" he had resigned.

Failure to inform the corporate regulator of changes to a company's shareholdings within 28 days carries a maximum penalty of $10,000. The party would not say if its company had breached the act.

Mr Walker said Liberal director Tony Nutt had told him a letter would be sent to ASIC on Thursday removing him as a shareholder.

Electoral Commissioner Tom Rogers said on Friday that the issue of Parakeelia "has been raised and we're aware of it".

Mr Walker's office said they would try to produce correspondence confirming he was told he was divested from all Liberal-linked companies in 2002.

Follow us on Twitter