Yahoo, too, is becoming a platform.

Following in the footsteps of Facebook, Google, and Microsoft, to name a few platform players, Yahoo is opening up to third-party developers. At the Web 2.0 Expo in San Francisco on Thursday, Ari Balogh, Yahoo's new CTO, announced the rewiring of Yahoo.

"We're literally in the process of rewiring Yahoo from the inside out to create a developer platform that will open up assets of Yahoo," Balogh said.

Balogh called the initiative the Yahoo Open Strategy and promised upcoming changes would make the consumer experience more social.

At the same time, Balogh denied that Yahoo was simply recasting itself to resemble Facebook. "We are not creating yet another social network," he said. "We are going to rewire the entire Yahoo experience to make it social in every dimension."

The first property Yahoo plans to open is Yahoo Search. The company's new Search Monkey developer platform will allow site owners to enhance the appearance of search results related to their sites with additional information. If it works, the platform will allow publishers and developers to make Yahoo Search more relevant to users by making new information available. It's possible, however, that Yahoo users won't want, or won't trust, third-party meddling with search results.

Search Monkey looks like a more flexible version of Google Co-Op in that it appears to allow developers more latitude in how they want to customize the Yahoo Search experience.

"Yahoo's open strategy is about not just opening up the search page," said Balogh. "It's about opening up all the properties of Yahoo."

Eventually, developers will be able to write applications that integrate with other areas of Yahoo, such as Yahoo Mail and the front page of Yahoo. In a blog post, Neal Sample, chief architect of platforms, said that the Yahoo Open Strategy will allow developers to use the Yahoo Address Book on third-party sites, for example.

"There's a massive, latent social network within Yahoo, and we're going to bring it to the surface," said Sample. "We're making Yahoo more social, but we're not building yet another social network. We already have an incredible social network, we just need to unlock it."

Never mind the denials. Yahoo is building yet another social network. But that's OK. Everyone is, because social computing provides a necessary filter (friends) to fight information overload, a lock-in mechanism (friends), and data valued by advertisers.

Conspicuously absent from Balogh's keynote was any mention of Microsoft, the would-be buyer of Yahoo, or of how the Yahoo Open Strategy might be viewed in Redmond.

It's tempting to speculate that Yahoo is embracing openness at least in part to spite Microsoft, which has supported openness mainly when doing so strengthened the market position of Windows.

But Microsoft is embracing openness, too, to some extent at least. It may be that the company has designs on Yahoo precisely because it too is headed where Yahoo is going, toward an open cloud-computing platform, powered by social data and targeted ad revenue.

Whatever the case, both Microsoft and Yahoo have to hurry up and go social before Google's friend list grows too large to compete with.