Twitter is on a #buyingspree.
The social media company announced late Monday it is buying MoPub, a mobile-focused advertising exchange, in its fourth major purchase of the year.
Terms of the deal were not disclosed. Published reports put the price at about $300 million or more, based an estimated values of Twitter's privately-held stock that is being used to make the purchase.
Twitter's statement said that MoPub's technology lets mobile application publishers manage their inventory of multiple sources of advertising.
In February it agreed to buy Bluefin Labs, a Cambridge, Mass., company that provides advertisers, ad agencies and TV networks with information about social media reaction to television shows.
In April Twitter announced the purchase of "We are Hunted," an Australian music streaming and recommendation service. That deal came a week before Twitter unveiled its own music app.