The Financial Times has reported a Google training exercise that went wrong to dummy advert.
It was meant to be a blank yellow rectangle.
People in the US and Australia.
Google's in-house ad-placing system.
He went out for one trainee and went to live order into the advert buying system.
The advert was placed at a higher rate of return than any other ad and was routed through several third-party exchanges.
"Said Google in a statement" as soon as we were aware of this.
It added that it would "honor" any payments to publishers which they incurred as a result of the mistake.
Google specifies that it would cost Google about $ 10m (£ 7.9m) in fees and clean up costs to rectify it.
Google said it would put controls in place to prevent the error being repeated.