Julian Assange appeared in court to give evidence over allegations he was spied upon while living at the Ecuadorian Embassy in London.
Footage from embassy CCTV cameras and documents, including private legal papers and a medical record, were allegedly offered to Spanish police during an undercover operation.
A Spanish security firm has been accused over the hack.
The case was launched in Madrid earlier this year.
Julian Assange - In pictures
Assange, 48, appeared at Westminster Magistrates' Courts in person on Friday.
The hearing was held in a closed court, but a small crowd of Assange's supporters were gathered outside the building in central London with banners and signs demanding his release.
Journalists were also denied entry to the courtroom.
Assange later gave evidence to a Spanish judge in the case via video link to Madrid.
Assange spent nearly seven years holed up in the embassy.
He is currently being held in HMP Belmarsh awaiting the outcome of an extradition request by the US.
The hearing was unconnected to the US extradition case.
In that he faces 18 charges including conspiracy to commit computer intrusion and is accused of working with former US army intelligence analyst Chelsea Manning to leak hundreds of thousands of classified documents.
Reporting by agencies.
