Microsoft on Friday announced the biggest acquisition in the software company’s history, buying online advertising company Aquantive for $6bn and making what it described as a “big bet” on its own long-term growth.

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Aline van Duyn discusses Microsoft’s hopes that Aquantive will help it create an online advertising force to rival Google and DoubleClick

The move – the largest deal in the advertising industry – continued the frenzy of interest in online advertising, coming a day after WPP bought 24/7 Real Media in a deal that valued the group at $649m. It also follows Google’s deal to buy DoubleClick for $3.1bn and Yahoo buying the RightMedia advertising exchange outright for $680m.

Microsoft has traditionally focused on small deals to acquire new technologies. The most it had paid previously was $1.45bn for the Danish software company Navision five years ago.

But Microsoft has been desperate to match Google’s advertising muscle and reportedly failed in an earlier multi-billion dollar bid for DoubleClick. It offered $66.50 a share for Aquantive, an 85 per cent premium to its closing price on Thursday.

Kevin Johnson, president of Microsoft’s platform and services division, said: “It is a big bet on advertising monetisation for the long-term growth of the company and this is a significant step forward.” He said the online advertising market would be worth $40bn this year and was growing at 20 per cent a year.

The acquisition means Microsoft will market its services to the wider internet.

Aquantive includes Avenue A Razorfish, one of the largest interactive advertising agencies. Tim Vanderhook, chief of the Specific Media online advertising network, said: “I think this will be sold off; it doesn’t really fit with Microsoft’s strategy and they can get a huge chunk back of the $6bn they paid.”

Microsoft has raised antitrust objections to Google’s acquisition of DoubleClick, which gives the search giant a strong grip on the growing online display advertising market. But Brad Smith, Microsoft general counsel, said Aquantive was complementary to Microsoft’s business and should not face any such objections, as it would promote competition.

Mr Johnson said the Aquantive deal would help Microsoft seize a significant opportunity in delivering services to a range of devices such as PCs, phones, game consoles and emerging media such as internet television.