Yahoo says it will buy Flurry Inc., which helps other companies make apps and design mobile ad campaigns.

Yahoo did not disclose how much it will pay for the San Francisco company, which also helps companies analyze the effectiveness of their advertising.

Flurry says its analytics are used by 170,000 developers. Yahoo says the acquisition will give Flurry the resources it needs to work with more developers. Yahoo Inc. says most of its users are visiting on mobile devices, and its mobile display and search revenue has more than doubled over the last year.

Yahoo's competitors have similar services, and the move could help the Sunnyvale, California company attract advertisers by creating ad campaigns and measuring their effectiveness.