In a move that stunned and dismayed supporters from Wall Street to Silicon Valley, tech stalwart and commercial printing heavyweight HP accused Autonomy's former management of "a willful effort to inflate the underlying financial metrics of the company in order to mislead investors and potential buyers".

The Autonomy related writedown came as HP announced a $6.9bn net loss for the fourth quarter, compared with a $239m profit for the same period in 2011, on a 6.7% net revenue decline to $30bn for the three month period. This pushed HP's full year net loss to $12.7bn on sales of $120.4bn.

HP added its Q4 commercial printer revenue was down 13%, and hardware units were down 15% year-over-year. But in a conference call with analysts, CEO Meg Whitman pointed out, "Indigo had a record quarter, and this is taking advantage of the move from analogue to digital, which I know that the printing group has talked about for many years at HP. I actually think we're seeing some of that, particularly in the Indigo space."

But it was the accusation of sharp accounting practices at Autonomy that stole the headlines - a fact that was not lost on Autonomy founder Mike Lynch who countered that HP was trying to distract investors from its worst results in its 70 year history.

In a statement announcing the writedown, HP said: "The majority of this impairment charge, more than $5 billion, is linked to serious accounting improprieties, misrepresentation and disclosure failures discovered by an internal investigation by HP and forensic review into Autonomy’s accounting practices prior to its acquisition by HP.

"As a result of that investigation, HP now believes that Autonomy was substantially overvalued at the time of its acquisition due to the misstatement of Autonomy’s financial performance, including its revenue, core growth rate and gross margins, and the misrepresentation of its business mix."

HP has accused Autonomy's former management - including Lynch, who was ousted in May - of artificially inflating revenue and gross margins by booking licensing deals as revenue and wrongly characterizing low-end hardware sales as software sales revenue.

In speaking with analysts, Whitman noted that the two people at HP who drove the $11 billion Autonomy acquisition, then CEO Leo Apotheker and the former chief strategy officer Shane Robison we’re also both gone from the company.

She conceded most of HP’s current board was in place for the Autonomy deal, but added: "What I will say is the board relied on audited financials, audited by Deloitte, not brand x accounting firm but Deloitte. And by the way, during our very extensive due diligence process, we hired KPMG to audit Deloitte, and neither of them saw what we now see after someone came forward to point us in the right direction."

This anonymous whistleblower, described by HP as "a senior member of Autonomy's leadership team", was said to have come forward following Lynch's departure with allegations of "a series of questionable accounting and business practices at Autonomy prior to its acquisition by HP".

Whitman concluded: "In the end, you have to rely on audited financials and we did, and we will now carry on. And as you know, we've reported this to the SEC, as well as to the Serious Fraud Office, and we will take it from here."