WhatsApp said ads will be targeted to users based on information like the user’s age, the country or city where they’re located, the language they’re using, the channels they’re following in the app, and how they’re interacting with the ads they see.

They will appear in only one part of the Meta-owned messaging service, it said. The move is potentially lucrative, while raising questions about user privacy.

The cofounders of WhatsApp resisted ads in the app for years, including after the company was acquired by Meta for $22 billion in 2014. Brian Acton and Jan Koum left the company in 2017 and 2018, respectively, and on Monday Meta introduced ads in the “Status” feature as well as sponsored Channels in the the “Updates” tab of WhatsApp.