Major deal. Here's the announcement. Working on the story now. More to come.

Update, 5:40 a.m.: Microsoft's planned acquisition of aQuantive is structured as an all-cash deal, at $66.50 per share. In addition to adding to Microsoft's advertising technology and relationships, this deal gives it another big boost in employees. From the news release: " aQuantive, which has approximately 2600 employees, will continue to operate from its Seattle headquarters as part of Microsoft's Online Services Business."

See the AP's coverage. Microsoft's conference call starts shortly. More to come.

Update, 5:50 a.m. Kevin Johnson, Microsoft Platforms and Services division president, confirmed on the call that the $6 billion purchase would be the biggest acquisition in Microsoft's history.

Update, 6:30 a.m. Microsoft has raised concerns over Google's proposed $3.1 billion acquisition of DoubleClick, saying that it could hurt competition in the online advertising market. Microsoft's aQuantive acquisition will also be subject to regulatory review. Here's what Brad Smith, Microsoft's general counsel, said on the subject during the conference call:

"We've consistently stated that, given the importance of this business to the future development of the Internet, we think it's very important that enforcement agencies fully study the competitive implications of acquisitions in this sector. ... Acquisitions of complementary assets, such as the Microsoft-aQuantive deal, normally do not raise antitrust concerns."

Update, 6:40 a.m. aQuantive posted a profit of $54 million last year on revenue of $442 million. To get a better sense for aQuantive's business, here's how the company broke down its business in its latest quarterly regulatory filing:

Digital Marketing Services (DMS)
Our DMS segment consists of Avenue A | Razorfish and a number of other international agencies. Avenue A | Razorfish is an interactive agency located in the United States that provides a full-service offering, including website development, interactive marketing and creative development and branding.

Digital Marketing Technologies (DMT)
Our DMT segment consists of Atlas, a provider of digital marketing technologies and expertise and recently-acquired Accipiter, a publisher-side ad serving technology provider. Atlas's software suite enables agencies and enterprise marketers to manage their entire digital marketing effort, including planning campaigns, displaying ads, search engine marketing and optimizing their websites. In addition, select publishers utilize Atlas to manage digital advertising inventory. Accipiter provides web publishers an inventory management solutions that enables the publishers' direct sales force to maximize revenue earned from premium display and text placements.

Digital Performance Media (DPM)
Our DPM segment consists of DRIVEpm, U.K.-based MediaBrokers and Franchise Gator. Both DRIVEpm and MediaBrokers are performance media and behavioral targeting businesses. DRIVEpm and MediaBrokers serve as intermediaries between online publishers and advertisers by procuring online advertising inventory from publishers and reselling that inventory to advertisers on a highly targeted basis. Franchise Gator is an extension of the performance media business, focused on the franchise industry, which addresses clients' needs for online leads.

Update, 7 a.m. Shares of aQuantive have soared on the news, while Microsoft shares are down. The purchase price, per share, is an 85 percent premium over aQuantive's Thursday closing price of $35.87. Chris Liddell, Microsoft's chief financial officer, was quizzed about the issue of the purchase price on the conference call. Here's what he said:

"As you know, we have done a large number of transactions over the last couple of years, something like 40. They've typically been in the smaller to medium size, and also as a number of people on the call know, we have walked away from transactions over the last few years, because we considered they haven't been strategically important enough to pay a premium for. In the case of aQuantive, we believe it is exactly the right company to buy, and hence we're willing to pay the value that we're talking about today. We have been very selective in our acquisition approach, and waiting for what we consider to be the most strategically important acquisition."