Details of the sale remain undisclosed but reports from TechCrunch have valued the acquisition at $10m.
Adku already works with major ecommerce sites Amazon and eBay. It was founded a year and a half ago in San Francisco by three former Google engineers.
Ajit Varma, co-founder and chief executive of Adku, wrote in a blog post: "We started talking to Groupon to bring our technology to more customers and quickly realised that we wanted to be a deeper part of a company."
Groupon, which uses the group-buying mechanism to offer daily deals at heavily discounted prices, was founded in Chicago in November 2008.
After turning down Google's $6bn offer to buy the business, .
It became the largest IPO by an internet business in the US since Google's in 2004, which at the time was valued at nearly $13bn.
In the UK, , after the regulator received complaints from the Advertising Standards Authority, among others.
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