Walmart Stores (WMT - Get Report) has discretely been fortifying its online advertising business, creating another revenue opportunity for the American retail giant.

The retailer's website has started to display banners ads by third party advertisers at a higher rate, KeyBanc's analyst Ed Yruma wrote in a note obtained by CNBC. 

"We believe Walmart recently began intensifying focus on its advertising business," Yruma wrote.

Additionally, Walmart has begun providing more in-depth data to its advertisers, including its in-store and online shopping information.

Shares of Walmart were lower in afternoon trading on Friday. 

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