One association of audiovisual producers has estimated the damages they caused to rights holders at more than €500 million ($560 million).
Created in 2008 by an intern at the University of Murcia in Spain's southeast, they became hugely popular in the Spanish-speaking world.
The trial comes after Spain earlier this year adopted a reform easing the closure of sites that violated intellectual property rights more than once.
Prosecutors say the websites “gave internet users access to audiovisual material protected by intellectual property rights”, providing weblinks to online users where they could watch or download films and series for free.
The founder, identified only as A.G. by prosecutors, earned money from advertising on the sites used by many in Spain and Latin America.
In a court document, prosecutors said the founder started the websites “for profit and knowing the activity was illicit”.
In April 2010, the founder sold the sites' domain names for €610,000 to three investors who are also on trial, say prosecutors.
Sold again in 2014, the three websites stopped providing links to illegal content.
Prosecutors are seeking a two-year jail sentence and a fine of around €4,000 euros for the four defendants, as well as the closure of the sites and compensation for two associations of rights holders and producers.
In 2016, a court ordered the closure of another Spanish website, football streaming site Rojadirecta.
It ruled it had breached the intellectual property of audiovisual groups that own the rights to broadcasting sporting competitions.
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