An AOL property

AOL, which has quietly languished outside the limelight as Google and Microsoft fight over Yahoo, just acquired buy.at.

The affiliate marketing network cost AOL $150 million, reports TechCrunch UK.

Buy.at is the fifth ad company AOL has bought in the past 12 months or so. Previous buys include Tacoda, AdTech, Third Screen Media, and Quigo.

Buy.at will operate as a business unit of AOL's Advertising.com, providing advertisers an alternative to traditional ad campaigns with a pay-per-action model.

Buy.at also focuses on social network marketing, long a missing piece in AOL's ad platform puzzle.

Earlier this week AOL bought Goowy, a widget creator.