Groupon has acquired Adku, an one-year-old start-up focusing on providing data to big retailers to make recommendations, for over $10 million.

Adku, which raised $1.5 million from investors in January of last year from Greylock Partners, True Ventures, Battery Ventures and AngelPad for a pre-money valuation of $5.25 million, has been in stealth mode ever since launching in early March 2011. The San Francisco-based start-up was a graduate of AngelPad's inaugural accelerator class in the fall of 2010. 

"We started talking to Groupon about two months ago," said Carlos Whitt, co-founder of Adku, in an interview. "The idea was that they could be a potential client. But we realized there was a lot more we could do if we joined them."

Whitt would not share many details about the start-up or transaction, only to say that Adku works with major retailers and is a company that's using big data for predictions and recommendations around demographics and location for e-commmerce.  

Founded by three ex-Googlers, Ajit Varma, Carlos Whitt and Jesse Shieh, Adku now has six employees - all in engineering roles. They'll all be moving over to Groupon's Palo Alto office, said Whitt.