Microsoft reportedly has been seeking to acquire a company that specialises in brokering and tracking online ads for some time. The software giant reportedly made overtures to online display advertising specialist DoubleClick earlier this year, though DoubleClick was ultimately acquired by Microsoft rival Google for $3.1bn in April.

Google's move was widely seen as a defensive play directed at Microsoft, which has declared an intention to gain ground on Google in online services and has committed billions of dollars to the effort.

Microsoft's acquisition of the company would build on some momentum reported when the company announced third-quarter financial results last Thursday. At that time, Microsoft reported a 23% increase in online ad revenue, though it did not offer specific sales figures.