John McAfee, the creator of the eponymous antivirus software, was found dead on Wednesday in a prison outside Barcelona. He was 75.

Over the past decade he gained notoriety for his ranting on social media, his involvement in a Central American criminal investigation and accusations from US authorities he was involved with pumping and dumping cryptocurrencies.

McAfee’s body was discovered in his cell hours after Spain’s National Court approved his extradition to the United States over multiple tax fraud charges.

Spanish newspaper La Vanguardia reported McAfee appeared to have died by suicide.

McAfee had been in Spanish custody since October on a June 2020 US indictment in which he was charged with failing to file four years of tax returns while concealing assets.

Then in March he was indicted and accused of fraud and money laundering over his use of social media to promote cryptocurrencies, which prosecutors said generated $13m in illicit gains for McAfee and a co-conspirator.

Nishay Sanan, McAfee’s attorney, said his colleagues in Spain confirmed McAfee had been found dead in his jail cell. Sanan claimed the US government had identified McAfee as a target and “tried to erase him, but failed”.

“John lived his life the way he saw fit,” Sanan said. “In the end that is all that matters. You don’t have to agree with his way — he did not care.”

Before his legal turmoil, McAfee was a pioneer of the cyber security industry.

He founded McAfee Corporation in 1987 in Santa Clara, California, and led the company as it dominated the market for antivirus protection of personal computers. Half of all Fortune 100 companies were using his software during that time.

McAfee resigned in 1994. Decades later he told the South China Morning Post that running the company was no longer fun as it grew to a huge corporation with thousands of employees.

Intel bought the company in 2010 and later rebranded all McAfee products as Intel Security. After his name was removed, McAfee told the BBC: “I am now everlastingly grateful to Intel for freeing me from this terrible association with the worst software on the planet.”

McAfee relocated to Belize in 2008 after his $100m fortune was reduced to $4m following a series of failed investments in property, real estate and bonds.

There he had one of his biggest conflicts with authorities in 2012 after the killing of a neighbour, Gregory Faull, a 52-year-old contractor.

McAfee’s home on the island of Ambergris Caye was searched after Faull was shot dead and police said they wanted to question him as part of a murder investigation.

He then sought asylum in Guatemala in 2012, claiming he was not on the run from authorities in Belize.

He turned to social media and public interviews to salvage his reputation, sending updates to Wired magazine, allowing two reporters from Vice magazine to accompany him and posting missives to his own website.

He discussed eluding police by burying himself in sand with a cardboard box and changing his appearance.

McAfee was expelled from Guatemala and arrived in Miami in December 2012. In an interview with Bloomberg News the day of his departure,

McAfee, then 67, said he was being forced out of Belize, but was “perfectly happy with the decision.” He apologised to Guatemala’s then-president for putting him in “a slippery position.” He was later ordered by a Florida judge to pay more than $25m to Faull’s estate.

In 2016 McAfee announced a run as a presidential candidate for the Libertarian Party, campaigning on a privacy-focused platform that included pushing for the US government to create a cyber security defence strategy. The party’s nomination was won by former New Mexico Governor Gary Johnson.

By 2017 McAfee had jumped on the Bitcoin bandwagon as chief executive officer of MGT Capital Investments. He promised to turn the former video game operation into a profitable cyber security firm by ramping up its Bitcoin mining business.

He stepped down later that year to lead a cryptocurrency company, Luxcore.

Part of his cryptocurrency venture included charging more than $105,000 per tweet to promote initial coin offerings.

McAfee later told his Twitter followers he had been forced to “go dark” on social media after receiving unspecified “threats” from the US Securities and Exchange Commission watchdog.

During the period from 2014 to 2018 McAfee failed to file US tax returns.

After eluding law enforcement, he was arrested and detained last October in Spain. From prison, McAfee was able to use Twitter to continue promoting cryptocurrencies, but also to share his experience.

In April, he tweeted: “This has been the most trying period in my life.”

In November 2019 McAfee took to Twitter to show off his latest tattoo on his right bicep. It read, “$WHACKD.”

In a related tweet, he wrote: “Getting subtle messages from US officials saying, in effect: ‘We’re coming for you McAfee! We’re going to kill yourself. I got a tattoo today just in case. If I suicide myself, I didn’t. I was whackd. Check my right arm.”

“Sometimes genius and madness aren’t far apart and it seems he unfortunately fell prey to his demons,” said Doug Clinton, managing partner at Loup Ventures.

John David McAfee was born on a US army base in the Forest of Dean, Gloucestershire, England, on September 18, 1945. His father was an American serviceman, his mother English.

He grew up in Virginia, where he recalled a childhood leading a local gang of boys. His father, however, who worked as a road surveyor, was an alcoholic and would beat him and his mother, who had a job as a bank clerk. When John was 15, his father shot himself.

McAfee graduated from Roanoke College, having studied mathematics, in 1967. He supported himself hawking magazine subscriptions and discovered he was a natural salesman, albeit most of his earnings went on alcohol.

He then began a PhD at Northeast Louisiana State University, but this came to an end when it was discovered he was sleeping with a student he was supervising. The pair subsequently married.

He then had jobs with some of the largest technological enterprises of the day, including Nasa and Xerox.

Like many in the industry, however, he had become a heavy user of drugs. In 1969, he had concocted a fake CV to get a position with Missouri’s railway company, which used an IBM computer to co-ordinate train schedules.

McAfee had begun to experiment with hallucinogens, which were still exerting their effect when he went to work. He ended up, in his words, “stark, raving mad”, hiding behind a rubbish bin in an alley, and never returned to the office.

He even took a year off to travel around Mexico peddling drugs. In 1983, however, he renounced his vices with the help of Alcoholics Anonymous and thereafter claimed to have remained sober.

After returning to the US in 2013, he settled in Tennessee with his third wife Janice, a former escort 40 years his junior.

There he had set up a technology incubator. Anonymity online became his chief preoccupation.

In 2014 — four years before the revelations about the harvesting of data collected by Facebook — he warned against the use of apps on smartphones. These, he said, were used to spy on people.

Last October McAfee was arrested at Barcelona airport when he was about to board a flight to Istanbul. He was found dead in prison last week.

His wife survives him.