The Consumer Protection and Defence Department (DPDC) fined the fixed and wireless telephony and broadband internet company after determining that its customers' browsing data had been sold, the justice ministry said in a statement Wednesday.
The fine was imposed after a DPDC investigation into an agreement between Oi, Brazil's largest telecommunications company, and British firm Phorm.
That accord provided for the development of a software programme called Navegador that registers customers' data traffic and creates a profile of internet users that Oi could then sell.
"The company, under the pretext of improving the browsing experience, hid from customers essential information about the service and its implications for privacy and the safety of their personal data," DPDC director Amaury Oliva was quoted as saying in the ministry statement.
"At no time were customers told that their browsing would be monitored by the company and that their profile would be sold to advertising companies," he added.
The amount of the fine was determined taking into account the criteria set forth in the Consumer Defence Code, the economic benefit received, the company's condition and the seriousness of the offence, the justice ministry said.
The proceeds from the fine will be deposited in a fund for reinvestment in actions to preserve the environment and public heritage assets and bolster consumer protection, the statement said.