UK entrepreneur Mike Lynch has denied new criminal charges against him, ahead of a court case in London on Monday over the sale of his firm Autonomy.
The civil case in London is over the £8.4bn sale of the software firm to Hewlett-Packard (HP) in 2011.
On Friday US prosecutors added three new criminal charges to their indictment against Mr Lynch.
He faces a new charge of securities fraud, as well as additional charges of wire fraud and conspiracy.
They are part of a 17-count indictment filed with the federal court in San Francisco.
"These are baseless, egregious charges issued on the eve of the trial in the UK, where this case belongs, and Dr Lynch denies them vigorously," a spokesman for the entrepreneur said.
In the UK case, HP is suing Mr Lynch and former Autonomy chief financial officer Sushovan Hussain for $5.1bn.
HP alleges that they inflated the value of Autonomy before selling the big data firm, but Mr Lynch and Mr Hussain deny the claims.
Who is Mike Lynch?
- A Cambridge graduate who built Autonomy up to be one of the top 100 UK public companies
- Has an OBE for services to enterprise
- Is a fellow of the Royal Society
- Was previously on the boards of the British Library and the BBC
Autonomy was founded by Mr Lynch in 1996. It developed software that could extract useful information from "unstructured" sources such as phone-calls, emails or video, and then do things such as suggest answers to a call-centre operator or monitor TV channels for words or subjects.
Before it was bought by Hewlett-Packard, it had headquarters in San Francisco and Cambridge.
In 2010, about 68% of Autonomy's reported revenues came from the US and elsewhere in the Americas.
HP and US prosecutors allege that Mr Lynch and other former Autonomy figures artificially inflated the software company's revenues and earnings between 2009 and 2011, causing HP to overpay for the firm.
But Mr Lynch has argued that HP used the allegations to cover up its own mismanagement of Autonomy after the 2011 deal.
If found guilty, Mr Lynch - who was once dubbed Britain's answer to Bill Gates - could face jail time in the US.