Buy.at is a network where advertisers can pay its member Web publishers based on user actions. The network also has an e-commerce platform where merchants can sell their products through third-party sites.

According to MediaPost, the purchase comes just several days after Microsoft's offer to buy Yahoo, which has aroused acquisition rumors for AOL. It also came a day prior to Time Warner's 1Q financial report, which is expected to include guidance on the future of AOL.

Targeting the largest marketers and ad agencies, AOL set up Platform-A last year to encompass its various ad networks. Platform-A works closely with Advertising.com, the AOL unit that matches online ad buyers to thousands of sites with extra ad space to sell.

"This acquisition further enhances Platform-A advertising offerings by enabling us to offer a new set of advertiser and publisher products, while also supporting our international strategy," said AOL Chairman and CEO Randy Falco in a statement, according to MediaPost.