Microsoft Corp's chief executive said on Thursday he did not rule out further acquisitions of a similar size to web advertising firm aQuantive.

We do not rule out any more deals like this. But this is something we are not doing every day, Microsoft CEO Steve Ballmer said at a press conference in Zurich.

The world's largest software maker bought Seattle-based Web advertising firm aQuantive this year for $6 billion.

Microsoft Advertising Steve Ballmer