Microsoft has bought Seattle-based digital marketing company aQuantive in a deal valued at over $6bn, nearly double yesterday's market valuation of the firm.

The purchase is another move in a grab by big players for the lucrative internet advertising market, following Google's $3.1bn DoubleClick acquisition.

Google's initiative sparked a bidding war, with Yahoo paying $680m for Right Media and WPP buying 24/7 Real Media for $637m.

"The advertising industry is growing at an incredible pace, moving increasingly toward online and IP-served platforms which dramatically increases the importance of software for this industry," said Microsoft chief executive Steve Ballmer.

"Today's announcement represents the next step in the evolution of our ad network from our initial investment in MSN, to the broader Microsoft network including Xbox Live, Windows Live and Office Live, and now to the full capacity of the internet.

"Microsoft is committed to creating a thriving advertising business and to partnering closely with all key constituencies in this industry to help maximise the digital advertising opportunity for all."

AQuantive will be integrated into Microsoft's MSN network, and its 2,600 employees will remain in their Seattle headquarters.

"AQuantive's mission has been to leverage the power of digital marketing services and technologies to drive measurable results for our clients," said Brian P. McAndrews, chief executive at aQuantive.

"Microsoft has set a leading example in prioritising industry partnerships, transparency, measurement and quality, and we look forward to combining forces and bringing the value of our combined assets to bear for the benefit of advertisers, ad agencies and publishers."

By taking over aQuantive's client base, Microsoft will open up a new pipeline for selling ads on both 3rd-party site and on its own Windows Live services.

"A large part of advertising is about connections," explained David Hallerman, a senior analyst for research firm eMarketer.

"It gives [Microsoft] that connection, which can help them sell search ads."

Hallerman told vnunet.com that the outcome of the deal will depend largely on how Microsoft implements aQuantive into its own business plans, particularly regarding its MSN ad service, which has been in direct competition with aQuantive.

"Probably the smartest move would be for Microsoft to fold aQuantive and MSN together."

To acquire aQuantive, Microsoft will pay $66.50 per share, a sharp increase from the $35.87 that the company's stock was trading at when the markets closed on Thursday.

Hallerman said that the purchase suggests Microsoft felt pressure to keep up with Google.

"It's a bit of a sign of a 'better buy it now or it will be too late' kind of strategy," he commented.

• Shaun Nichols contributed to this story