Spanish police have arrested a former employee of HSBC's Swiss private bank who was convicted of industrial espionage after leaking clients' tax information, Spain's Interior Ministry has said.
Herve Falciani, a French citizen, fled Geneva to France in 2009 after HSBC discovered the leak and put him under investigation. He says he is a whistleblower who wanted to help governments track down tax evaders.
France, Austria, Belgium, Spain and Argentina launched investigations based on the information, but Switzerland's highest court rejected a French request for help in a case saying the data was stolen and therefore inadmissible.
Falciani has been living in France, which does not usually extradite its own citizens and where there are no legal proceedings against him.
But police in Spain, learning that he was due to deliver a speech at a Madrid university, acted on an international detention and extradition order from Swiss authorities dated 19 March, the Interior Ministry said.
Mr Falciani was arrested on Tuesday close to the Universidad Pontificia de Madrid where he was due to speak on "When telling the truth is heroic".
In 2015, a Swiss court sentenced Falciani to five years in prison for aggravated industrial espionage. The Swiss attorney general was not immediately available to comment on Tuesday.
A spokesman for Spain's High Court declined to give additional information or say what might be the next steps.
On a previous trip to Spain, in 2012, Mr Falciani was detained on an international arrest request but Spain's High Court ruled against his extradition as the charges he faced in Switzerland were not considered crimes under Spanish law.