MADRID/BOSTON, June 10 (Reuters) - Spanish police arrested three men suspected to be members of the hacker group Anonymous on Friday, charging them with organizing cyber attacks against the websites of Sony Corp (6758.T), banks and governments -- but not the recent massive hacking of PlayStation gamers.

Anonymous responded by threatening to retaliate for the arrests: "We are Legion, so EXPECT US," the group said on its official Twitter feed.

Spanish police alleged the three "hacktivists" helped organize an attack that temporarily shuttered access to some Sony websites. They were not linked to two massive cyber attacks against Sony's Playstation Network that resulted in the theft of information from more than 100 million customers.

Police also accused the men of launching cyber assaults on Spanish banks BBVA (BBVA.MC) and Bankia, and Italian energy group Enel SpA (ENEI.MI).

The arrests are the first in Spain against alleged members of Anonymous, following the detention of others in the United States and Britain. Police told Reuters all three men were Spanish and in their 30s. One worked in the merchant navy.