Joseph O'Connor, 22, was arrested in the coastal resort town of Estepona, Spain, on an arrest warrant accusing him of involvement in a July 2020 hack of more than 130 accounts, and of hacks that prosecutors said took over user accounts on the TikTok and Snapchat apps. Prosecutors also accuse O'Connor of cyberstalking a juvenile.
A criminal complaint filed in federal court in the Northern District of California charges O'Connor with crimes including cyberstalking, making extortive and threatening communications and intentionally accessing a computer without authorisation.
It was not immediately clear if O'Connor had a lawyer, although in prior interviews he has denied wrongdoing.
During the high-profile security breach a year ago, fake tweets were sent from the accounts of Barack Obama, Joe Biden, Mike Bloomberg and a number of tech billionaires including Amazon's then-CEO Jeff Bezos, Microsoft co-founder Bill Gates and Tesla CEO Elon Musk.
A Florida teenager was sentenced in March to three years in prison for his role in the hacking operation. Graham Ivan Clark pleaded guilty to multiple fraud charges as part of a deal with Hillsborough County prosecutors.
Andrew Warren, the Florida state attorney who prosecuted Clark, told the AP last year he considered him the mastermind of the plot.