ZDNet, San Francisco, announced Tuesday it has acquired search engine maker FerretSoft L.L.C. in a cash and stock deal valued at about $23 million. ZDNet plans to use FerretSoft's scalable technology to expand the portal's ability to help users locate information across the Web. ZDNet will offer FerretSoft utilities as downloadable desktop search agents. They also will be integrated throughout ZDNet sites. ZDNet plans to use its own advertising sales force to continue building this model by selling search keywords and integrating FerretSoft's ad inventory with its sales program.