Seattle-based 5to1, a developer of advertising network tools and operator of an advertising network, has been acquired by Yahoo. Financial terms of the acquisition were not disclosed. Yahoo is using the acquisition to build out its publisher partnerships and inventory. 5to1 was venture backed by Prism Ventureworks and Fuse Capital, and was headed by James Heckman. Yahoo said 5to1 will join its Ad Marketplaces group.