Twitter announced on Monday that it’s acquiring mobile ad startup TapCommerce. Re/code’s Ina Fried broke the news about the acquisition earlier this afternoon, reporting that the deal price was $100 million. (Twitter declined to provide a price). TapCommerce helps mobile businesses retarget their ads, i.e., target ads based on previous user activity — something that’s become common for desktop web advertising but not really on mobile, due to the lack of cookies. (Co-founder and CEO Brian Long has said TapCommerce is able to retarget using “large amounts of data coupled with sophisticated statistical analysis”) For example, an e-commerce app could use retargeted ads to convince a lapsed user to return, maybe by promoting new sales and promotions. It seems like TapCommerce’s technology could offer Twitter way to improve the mobile app install and engagement ads that it announced on Monday.