Yahoo said it is opening up its new advertising system - code-named Panama - for testing by newcomers who sign up for a Yahoo advertising account, reports Reuters; since October, the system had been available, by invitation, to those who were already Yahoo advertisers.

Yahoo is introducing the system in stages before it's officially launched in the U.S. in the first quarter of 2007. Thereafter, Yahoo will extend the new ad system into international markets.

"The systems are obviously at a level of scale, performance and stability we think we can take on all comers," Steve Mitgang, SVP of Yahoo's advertising products and platforms unit, told Reuters.

"In the past two months we have gotten nothing short of extraordinarily positive responses," he said.