Tens of millions of users who visit Google sites use a browser loaded with malicious add-ons, research suggests.
Most rogue extensions bombard people with ads, but the most malicious steal login names and other valuable data.
Carried out by security experts and Google, the project analysed more than 100 million visits to the search giant's sites.
It led to Google purging almost 200 bad extensions from its online catalogues of browser add-ons.