Spanish investigators Thursday probed the death of John McAfee who was found in his prison cell after an apparent suicide following a court decision approving his extradition to the US on tax evasion charges.

The body of the 75-year-old founder of the anti-virus McAfee software was discovered at around 7:00 pm on Wednesday in his cell in the Brians 2 penitentiary near Barcelona in what a prison service spokeswoman said was a death "apparently from suicide".

Catalan legal officials confirmed it was McAfee, who had been held at the facility since his arrest in early October as he was about to board a flight to Istanbul.

His body was taken away by judicial officials who opened an investigation to determine the cause of death, a spokeswoman for Catalonia's justice ministry told AFP on Thursday.

"There was a death which suggested suicide but confirmation must come through the autopsy," she told AFP, saying it could be a matter of days before a postmortem would be carried out.

According to an indictment filed in a US court, McAfee was alleged to have deliberately failed to file tax returns between 2014 and 2018, despite earning millions from consulting work, cryptocurrencies and selling the rights to his life story.

If convicted, he could have faced up to 30 years in prison.

"Guards and medical staff intervened immediately to perform resuscitation measures but doctors eventually certified his death," the Catalan justice department said in a statement.

The US government said McAfee had failed to pay tax on 10 million euros of earnings
The US government said McAfee had failed to pay tax on 10 million euros of earnings AFP / Fred DUFOUR

McAfee was found dead just hours after a Spanish court said it had approved his extradition to the United States in a decision which could have been appealed.

According to the US extradition request filed in November and quoted in the ruling, McAfee earned more than 10 million euros ($12 million) in 2014-18, but never filed a tax return.

"To conceal his income and assets from the Internal Revenue Service... the defendant ordered part of his income to be paid to straw men and placed property in their names," it said.

Since making a fortune in the 1980s with the antivirus software that still bears his name, McAfee had become a self-styled cryptocurrency guru, claiming to make $2,000 a day.

McAfee in 1987 founded the computer security software company and ran it for seven years before resigning.

His life after that became a headline-grabbing mix of controversies involving drugs, weapons and even murder.

John McAfee was accused by a US court of failing to pay tax on 10 million euros of earnings
John McAfee was accused by a US court of failing to pay tax on 10 million euros of earnings AFP / FRED DUFOUR

McAfee had more than one million followers on Twitter, where he described himself as a "lover of women, adventure and mystery".

In a tweet on June 16, he said the US authorities believed he had "hidden crypto".

"I wish I did," he added. "My remaining assets are all seized. My friends evaporated through fear of association. I have nothing. Yet, I regret nothing."

Since his arrest, his wife Janice has complained that he was "not doing well" in jail and had faced delays in getting "proper medical care".

"The US authorities are determined to have John die in prison," she tweeted on Sunday, adding: "There is no hope for him ever having a fair trial in America."

McAfee moved to Belize in Central America and made headlines when his next-door neighbour was mysteriously murdered in 2012. The crime was never solved.

McAfee claimed he was nowhere near the victim at the time, but local police have wanted to interview him as a person of interest in the case.

After the police found him living with a 17-year-old girl and discovered a large arsenal of weapons in his home, McAfee disappeared.

"I am not a madman," said the British-born former NASA programmer whose anti-virus company was bought by Intel in 2010.

"I am eccentric, gracious, attentive, kind, humorous. We humans are funny creatures."

The dead neighbour's family later filed a wrongful death suit against McAfee and in 2019 a Florida court ordered him to pay them more than $25 million.

A documentary titled "Gringo: The Dangerous Life of John McAfee" released in 2016 focused on his life in Belize.

In 2015, McAfee was arrested in the United States for driving under the influence and a year later, made an unsuccessful run for president.

From a political perspective, he advocated for ramping up defences against cyberattacks from China and Russia, and ending the war on drugs.