Terms weren't disclosed. In February, Viacom sites worldwide drew 76.6 million unique visitors 15 or older, says Internet metrics company ComScore.
Viacom had little choice. Having recently sued Google for copyright infringement on YouTube, Viacom couldn't very well shake the hand it's biting. That left Microsoft and Yahoo, and Yahoo is better established in search marketing.
Before Yahoo launched its Panama ad platform in February, companies that bid the most money for keywords received the highest ad placement on Yahoo search results pages. But Google proved that giving some preference to better-performing ads resulted in higher revenue. So Yahoo built that capability--ad quality measurement--into Panama to boost ad revenue.
Shortly after Panama was launched, ComScore reported an improved click-through rate for Yahoo ads, providing some validation. Now with Viacom onboard, Yahoo's prospects look even better.