In November HP revealed that it has taken a multi-billion dollar accounting charge on the Autonomy acquisition and asked US and UK authorities to investigate "accounting improprieties".

The revelation followed an internal investigation, which found what "appears to have been a wilful effort on behalf of certain former Autonomy employees to inflate the underlying financial metrics of the company in order to mislead investors and potential buyers," claimed the tech giant.

The SEC and UK Serious Fraud Office are looking into the claims and have now been joined by the Department of Justice, which opened its own probe at the end of November, a regulatory filing shows.

"We continue to believe that the authorities and the courts are the appropriate venues in which to address the wrongdoing discovered at Autonomy," says the firm.

Autonomy founder Mike Lynch, who left soon after the takeover, responded to the news by issuing a statement insisting that "these allegations are false".

"It is extremely disappointing that H-P has again failed to provide a detailed calculation of its $5 billion write-down of Autonomy, or publish any explanation of the serious allegations it has made against the former management team, in its annual report filing today," adds Lynch.