It is thought agencies that work with Microsoft were notified of the news yesterday.
Microsoft has complex agency arrangements and works with various shops on different parts of its business.
Interpublic Group’s UM runs the bulk of the global media account, while Microsoft works with Starcom MediaVest Group in its largest market, the US.
MDC’s Crispin Porter & Bogusky is one of Microsoft’s lead creative agencies globally, and created the "I’m a PC" ads that ran from 2008. The agency’s UK office launched the Windows Phone in the UK and has worked on Xbox in Europe.
WPP’s Wunderman also has substantial parts of the Microsoft business and works on creative, especially execution. Wunderman UK picked up the EMEA advertising account for Xbox last year.
Publicis Groupe’s Razorfish also works on some global digital business, while in the UK, Microsoft also works with Beattie McGuinness Bungay.
A Microsoft spokeswoman said: "Microsoft doesn’t comment on rumour or speculation."