The US company paid an undisclosed sum for UK-based affiliate network buy.at, which will now operate as a wholly owned business unit of AOL’s online advertising arm Advertising.com.

The deal provides an exit for private equity firm DFJ Esprit, which had invested $14.4 million (£7.4 million) in buy.at.

Founded in 2002, the acquired company enables “affiliate” websites to partner with advertisers, which pay only when a user directed from the affiliate site takes action. This action might involve making a purchase or signing up for a free trial.

According to AOL, buy.at has reaped the rewards of an early focus on social networking websites, in particular travel-focused website WAYN.

AOL chairman and CEO Randy Falco says: ‘This acquisition further enhances our… advertising offerings by enabling us to offer a new set of advertiser and publisher products, while also supporting our international strategy.’

With offices in London, Newcastle and New York, buy.at (the trading name for Perfiliate Technologies) has 70 staff and serves 200 e-commerce clients.