Facebook and Instagram are reportedly 'rewriting websites' visited by their users so they can follow them around the web.

Research from an ex-Google engineer claims that the social networks 'inject' other websites with a tracking code whenever a link is opened through their in-app browser.

This means Facebook and Instagram can monitor everything from your Internet history to your 'passwords, addresses, and credit card numbers'.

Meta has hit back at the claims saying that the tracking code follows users' privacy preferences, and that the data gathered is only 'aggregated' for use in targeted advertisin