Former Barcelona president Josep Maria Bartomeu was reportedly arrested following a raid at the club's offices on Monday.
His adviser Jaume Masferrer, the club's CEO Oscar Grau and head of legal services Roman Gomez Ponti were also among those arrested.
"Given the entry of the local police at the club's offices, per a court order relating to the hiring [of a third-party company] and monitoring services of social networks, FC Barcelona has offered its full support to judicial and police authorities and collaborated with them to clarify the facts that are the subject of the investigation," released the club in a statement.
Police were searching for evidence that Bartomeu used a third-party service to smear players and potential presidential candidates.
Barcelona were cleared for any wrongdoing in an external audit by PricewaterhouseCoopers, with Spanish police opening up their own investigation.