A Dutchman accused of mounting one of the biggest attacks on the internet used a "mobile computing office" in the back of a van.
The 35-year-old, identified by police as "SK", was arrested last week.
He has been blamed for being behind "unprecedentedly serious attacks" on non-profit anti-spam watchdog Spamhaus.
Dutch, German, British and US police forces took part in the investigation leading to the arrest, Spanish authorities said.
The Spanish interior minister said SK was able to carry out network attacks from the back of a van that had been "equipped with various antennas to scan frequencies".
He was apprehended in the city of Granollers, 20 miles (35km) north of Barcelona. It is expected that he will be extradited from Spain to be tried in the Netherlands.