Microsoft has admitted that the premium price of $6bn (£3.04m) it paid to acquire aQuantive is a "big bet" on the internet advertising market.

Analysts said the move was a bid by Microsoft to become a major player in the online display ad market and questioned where today's deal leaves Yahoo!.

Today's deal, by far the largest acquisition in Microsoft's history, will lead to the launch of an internet-wide advertising operation offering what the company claims will be a "complete end-to-end solution for advertising".

"We are willing to use the strength of our balance sheet when we consider it necessary to drive growth ... at times we will make strategic bets where we think it is necessary," said Christopher Liddell, the Microsoft chief financial officer.

Mr Liddell added that Microsoft was involved in a competitive bid to acquire aQuantive, although the names of rival bidders were not revealed.

When asked about the difference between this deal and Google's acquisition of DoubleClick, Brad Smith, the Microsoft senior vice-president and general counsel, accused Google of decreasing competition in the market.

"The difference is very straightforward. The Microsoft/aQuantive transaction will promote competition and the Google/DoubleClick transaction will reduce competition," he said.

"Consider on the one hand that aQuantive today is in three businesses and Microsoft today is in none of those businesses.

"Google and DoubleClick in contrast have strongly overlapping businesses in serving ads to third-party web publishers on the internet."

Mr Smith added that Microsoft believed that after the DoubleClick deal Google controlled 80% of the internet advertising market.

Microsoft is aiming to gain a slice of a global online ad market it says is worth $40bn (£20.2bn) a year, with 20% annual growth expected through to 2010.

"It is a big bet on ad monetisation for the long-term growth of the company and this is a big step forward," said Kevin Johnson, the Microsoft president of platforms and services.

Ian Maude, an analyst at Enders, said he believed today's deal was a significant strategic move that would be a blow to Yahoo!.

"Microsoft hasn't given up on search, but Google practically owns that market, so it is now going hard now into the display ad market," Mr Maude said.

"This strategic move means that it is less likely that Microsoft will bid for Yahoo! as it has to swallow this enormous acquisition.

"Yahoo! will be concerned because it has to deal with Google as a competitor on the search front and now perhaps Microsoft in display ads where, traditionally, Yahoo! has been the strongest player among the portals on display ads."

Mr Maude said an obvious move for Yahoo! may be to strengthen its relationship with eBay.

Yahoo! currently handles the search advertising deal for eBay in the US, while Google handles the auction website's international business.

Microsoft has been building up its expertise in delivering advertising to emerging media recently.

Last year Microsoft acquired in-game advertising company Massive for several hundred million dollars. It has also recently acquired European mobile advertising company ScreenTonic.

Microsoft will integrate aQuantive's advertising tools - Atlas and DRIVEpm - with its own products, such as the advertising delivery service adCenter that it launched around a year ago.

Analysts questioned whether Microsoft would hold on to aQuantive's digital ad agency network Avenue A/Razorfish, which owns London agency DNA.

Microsoft has a cash and investment warchest of $35bn (£17.7bn).

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