He was detained on Saturday as he was about to board a flight to Istanbul with a British passport, the source told Reuters, adding that he would be transferred to Spain’s capital Madrid to face an extradition process.

US federal prosecutors unsealed an indictment on Monday against McAfee over charges that he evaded taxes and wilfully failed to file returns.

That came shortly after the Securities and Exchange Commission revealed it had brought civil charges against McAfee, alleging he made over US$23.1 million in undisclosed compensation from false and misleading cryptocurrency recommendations.

He is alleged to have earned millions in income from promoting cryptocurrencies, as well as through consulting work, speaking engagements, and selling the rights to his life story for a documentary.