Brazilian state prosecutors in Rio de Janeiro opened a formal investigation into Google over pedophilia, defamation and false identity on its social networking site Orkut, O Estado de S. Paulo newspaper reported on Wednesday.

The Rio de Janeiro state prosecutor's office will give Google 120 days to implement a system that stores Internet protocol addresses, making it easier for authorities to track down images and pages that could be considered as complicit to a crime, Estado said.

These mechanisms already exist, but Google only stores user information for 30 days, Estado quoted Rodrigo Mascarenhas, a top prosecutor, as saying. It is a problem the police face when they investigate a crime.

Messages left for a Sao Paulo-based Google spokesman seeking a comment on the Estado story were not immediately returned.

The principal target of the measure is crimes of pedophilia, he added. Google must also fund a media campaign to promote responsible use of the Internet, Estado reported the prosecution saying.

(Reporting by James Matthews: Editing by Guillermo Parra-Bernal and Maureen Bavdek)