Microsoft has purchased aQuantive in its biggest and most expensive acquisition to date.

The $6 billion buy gets Microsoft a major presence in the online digital advertising market.

aQuantive has three divisions, Avenue A | Razorfish, Atlas Solutions and DRIVE Performance Solutions and Microsoft has set up a new business group to incorporate them.

The new Advertiser and Publisher Solutions (APS) Group will also encompass Atlas, DRIVEpm and Microsoft AdCenter.

Google, Yahoo and AOL have already bought, or are in the process of acquiring companies that operate online advertising

Microsoft paid 85% more per share than aQuantive was valued at, which critics suggests shows how desperate the software giant it to get into the lucrative online ad area.

Microsoft said the deal will "provide the advertising industry with a world-class advertising platform across devices and media that will create the best experiences for users, advertisers and publishers".