Twitter is moving deeper into mobile advertising with the purchase of MoPub, a startup focusing on mobile ad exchanges. The acquisition announced late Monday was estimated to be worth some $350 million, according to the technology news site TechCrunch. "MoPub's technology lets mobile application publishers manage their inventory and optimize multiple sources of advertising -- direct ads, house ads, ad network, and real-time bidding through the MoPub Marketplace," Twitter's Kevin Weil said in a blog post. "The two major trends in the ad world right now are the rapid consumer shift toward mobile usage, and the industry shift to programmatic buying. Twitter sits at the intersection of these, and we think by bringing MoPub's technology and team to Twitter, we can further drive these trends for the benefit of consumers, advertisers, and agencies." Weil said Twitter also plans to use MoPub's technology "to build real-time bidding into the Twitter ads platform so our advertisers can more easily automate and scale their buys." Twitter earlier this year began to allow ads to be targeted at users based on the words written in tweets. The fast-growing social network is expected to earn $582.8 million globally in ad revenue this year and nearly $1 billion next year, according to industry tracker eMarketer. It remains privately held, but a number of reports indicate the company may launch an initial public offering.