John McAfee Dies in Spanish Prison

By 2015, he was back in the United States and, after an arrest in Tennessee on gun and drunken-driving charges, ran for president as a Libertarian, with his campaign video declaring, “Here’s to the crazy ones.”

Last October, the Securities and Exchange Commission accused Mr. McAfee of promoting initial coin offerings — deals for cryptocurrencies — on Twitter without disclosing that he had been paid to do so. The S.E.C. said Mr. McAfee had pretended to be independent and impartial but had received more than $23 million for stirring up interest in the offerings.

Mr. McAfee grew up in Roanoke, Va., the son of a road surveyor and a bank teller in an unhappy marriage. He said in press reports that his father was a severe alcoholic who beat him and his mother, and who fatally shot himself when Mr. McAfee was 15.

“Every day I wake up with him,” Mr. McAfee told a reporter for Wired magazine in 2012. “Every relationship I have, he’s by my side; every mistrust, he is the negotiator of that mistrust.”

McAfee Associates, the software company he founded, was once a household name in computer security. He started it in 1987 in his small house in Santa Clara, Calif., in response to the news of a Pakistani computer virus called Brain, thought to be the first to attack personal computers. Mr. McAfee said that, at the time, it reminded him of the way his father would suddenly attack him.

His plan was to create an antivirus program and give it away on computer bulletin boards, with the hope that users would install it on their computers at work. They did, and the companies paid licensing fees, giving Mr. McAfee revenues of about $5 million a year by 1990.

McAfee Associates went public in 1992, making its founder’s stock worth $80 million, but he resigned in 1994. The company’s rise to prominence continued without him. Intel, the computer chip maker, bought the company in 2010 for $7.7 billion, then sold its majority stake to an investment firm six years later.