'When you bundle bots, clicks fraud, viewability and the lack of transparency [in automated ad buying], the total digital-media value equation is being questioned and totally challenged,' says Bob Liodice, chief executive of the Association of National Advertisers trade group. Advertisers are beginning to question if they should increase their digital ad budgets, he says.

‘The clients we work with would love to spend more money in digital,’ says Quentin George, a co-founder of ad-technology consulting firm Unbound. ‘But until we give them more control and transparency on how the money is being spent, they will continue to have questions and hold money back.’