http://blogs.wsj.com/cmo/2015/06/29/aol-takes-over-majority-of-microsofts-ad-business-swaps-google-search-for-bing/
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Under the AOL pact, Microsoft's Bing search engine will power search results and advertising on AOL's properties for 10 years. Bing is displacing Google Inc., which had long provided search technology for AOL.
For AOL and its new parent Verizon Communications Inc. – which recently completed a $4.4 billion acquisition of the company – the Microsoft partnership will give it a lot more ad inventory to work with as it tries to become a bigger force in the digital ad industry.
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Microsoft isn't exiting the ad business entirely – it will continue to sell search ads. The dramatic scaling back of its ambitions has been years in the making. Back in 2006, then-Chief Executive Steve Ballmer declared in a famous speech that advertisers, not software developers, were the backbone of the company. The following year Microsoft shelled out $6.3 billion to acquire the online advertising firm aQuantive, which was aimed at helping it compete with Google.
Empires like Google don't fall all at once, they crumble away a little at a time. AOL was due for a refresh and maybe they will do a better job at display ads.