After Google acquired DoubleClick for $3.1 billions, Microsoft is striking back. The Redmond company has acquired digital marketing firm aQuantive for 6 billion dollars in a bid to prevent Google's total domination of the online advertising market.

aQuantive, which was founded in 1997, encompassing three primary brands: Atlas provides a set of advanced tools for both advertisers and publishers, DRIVEpm provides services to publishers and advertisers that match advertiser campaigns with publisher inventory and Avenue A | Razorfish, one of the largest interactive ad agencies in the world, providing advertisers with industry-leading digital marketing consultation, media planning and buying, and creative services.

aQuantive is Microsoft's largest-ever purchase and came at a high cost to the software giant - a 66.50 dollar per share offer that is 85 per cent higher than aQuantive's closing price on Thursday.

"The advertising industry is evolving and growing at an incredible pace, moving increasingly toward online and IP-served platforms, which dramatically increases the importance of software for this industry," said Steve Ballmer, chief executive officer of Microsoft. "Today's announcement represents the next step in the evolution of our ad network from our initial investment in MSN(R), to the broader Microsoft network including Xbox Live, Windows Live and Office Live, and now to the full capacity of the Internet. Microsoft is intensely committed to creating a thriving advertising business and to partnering closely with all key constituencies in this industry to help maximize the digital advertising opportunity for all."

The purchase consolidates Microsoft's position in display ads that use sound and video, an area where the company still ranks ahead of Google, which dominates the market for ads linked to search terms.

"Because this space is so profitable and so important, we're seeing Microsoft make these type of investments," analyst Michael Gartenberg told Bloomberg News

aQuantive, which has approximately 2600 employees, will continue to operate from its Seattle headquarters as part of Microsoft's Online Services Business. The deal is expected close in the first half of Microsoft's fiscal 2008. The acquisition is not expected to significantly affect the company's prior financial guidance.