Yahoo has agreed to pay $300m (£149m) for one of the world's largest online advertising networks.

BlueLithium's behavioural targeting monitors the activities of people surfing its sites, allowing advertisers to be more precise in their promotional campaigns.

It is currently the second largest ad network in the UK and the fifth largest in the US, with more than 145 million visitors each month.

Yahoo says that the acquisition will provide its clients with detailed feedback on user activity, allowing for a wider range of marketing strategies.

'BlueLithium's products, technology and team will be an integral part of our drive to build the industry's leading advertising and publishing network,' said Yahoo chief executive officer Jerry Yang.