In the midst of its continuing effort to buy Yahoo for $41 billion, Microsoft today launched Engagement Mapping, a new initiative that rolls in technology from aQuantive.

With Engagement Mapping, an effort slated to enter beta testing on March 1, Microsoft hopes to replace "last ad clicked," a conventional approach that connects sales, leads, and traffic to the last ad that a visitor clicked on while traversing the Web.

In contrast, Engagement Mapping is designed to show how ongoing exposure to a display, rich media, or search site ad influences a person's buying behavior, across the frequency and reach of the ad exposure and the size and format of the ad, according to Brian McAndrews, who formerly headed up aQuantive and is now senior VP of Microsoft's Advertiser & Publisher Solutions (APS).

Customers and advertising agencies testing the technology have included Monster Worldwide, BKV, Best Western International Inc., and McKinney, for example.

Last May, Microsoft acquired the Australian advertising platform provider for $6 billion, to beef up its online advertising arsenal. The aQuantive buyout constituted its largest to date. Just prior to their consummation, Microsoft was also rumored to be bidding for a small online ad agency called 24/7 Real Media, but the WPP Group snapped up that ad agency for $649 million.

Microsoft's other acquisitions in the online advertising space have included TellMe, a specialist in voice-enabled mobile marketing, noted Rob Helm, an analyst at Directions on Microsoft.

Although probably best known for its ad agency Avenue A/Razorfish, aQuantive also created Atlas, a platform for optimizing ad campaigns, and DRIVEpm, a tool for matching ad campaigns to available publisher inventory.

Yahoo, a company particularly strong in display advertising, and Google have also been busily gobbling up smaller companies in online advertising over the past few years, often trying to integrate the technologies of the acquired properties into their own online ad platforms.

"And there's planty of money out there [among most of the large players] for more acquisitions right now. Lots of money," according to Helm.