Microsoft has finally completed the acquisition of aQuantive for nearly $6 billion yesterday. It is the most expensive acquisition in Microsoft’s corporate history. Hence, it is bound to raise many eyebrows in the Silicon Valley, for Microsoft is heading towards a major search war battle against Google and Yahoo!.

Microsoft paid $6 billion in May this year. The Federal Trade Commission (FTC) has approved Microsoft’s aQuantive acquisition by clearing the antitrust regulatory hurdle last month.

Microsoft is now forming a new Advertiser and Publisher Solutions (APS) Group, which includes bigwigs of both the companies. The former aQuantive CEO, Brian McAndrews will be heading the group. The group will develop strategies in the areas relating to monetization engine, MSN.com portal and Windows Live services.

The aQuantive acquisition symbolizes software giant’s long-term vision to compete against Google not only in the search advertising market but also in the other areas such as media planning, video on demand and IPTV.

It is an open secret that Microsoft’s Live Search is not so sophisticated as compared to Google. Yahoo! is also a step ahead from Microsoft in terms of searches performed each month. According to latest comScore data, Google generates half of the US-based online searches in May, in comparison to meager 10.3% by Microsoft sites.

We should not overlook Google, who has a major share in the online ad revenue. It is now in constant effort to acquire aQuanitive’s arc rival Double Click for $3.1 billion in cash, though there are some constraints at the FTC level.