Four months after canning Carol Bartz, its last CEO, Yahoo Wednesday morning named PayPal president Scott Thompson its fourth CEO in under five years. He starts January 9.

Acting CEO Tim Morse will go back to being CFO.

According to Yahoo chairman Roy Bostock, Thompson is expected to "restore the energy, focus, and momentum necessary to grow the core business and deliver increased value for our shareholders." Yahoo shares dipped on the news.

It will take Thompson, a technologist with no advertising, media or turnaround experience, a while to get up to speed.

He said his "immediate focus will be on getting to know the entire team and hearing more from all Yahoos, working closely with the engineers and product teams, and diving deeply into our products and services to learn more about what our more than 700 million users find most engaging and useful. I will also be working directly with our region leaders and sales teams globally to get a clearer understanding of the needs of our advertisers and publishers. Clearly, speed is important but we will attack both the opportunity ahead and the competitive challenges with an appropriate balance of urgency and thoughtfulness. I cannot wait to get started."

Thompson is expected to work with Yahoo's dysfunctional board. Bostock made clear that "Scott's primary focus will be on the core business, and as CEO and director, he will work closely with the board as we continue the strategic review process to identify the best approaches for the company and its shareholders. As part of this process, Yahoo is considering a wide range of opportunities for the company's business, as well as specific investments or dispositions of assets."

The company is supposed to be entertaining proposals to sell off its position in Yahoo Japan and part of its 40% holding in Alibaba for billions of dollars. Alibaba has also said it would like to buy all of Yahoo and has reportedly been putting the financing together. Thompson's appointment apparently signals that Yahoo won't be sold.

A minority stake in Yahoo could still go to private equity investors. There are two proposals on that table, one from Silver Lake, another from TPG Capital, and rumors that Google and Microsoft could also take a run at the struggling Internet pioneer.

Thompson said on a conference call that he is convinced Yahoo's core business assets are stronger than people think, ticking off its traffic, brand, technology and access to data. Sounds like data's probably his strong suit. He also has mobile ambitions. Yahoo flubbed mobile.

Up against Google and Facebook sales growth and vision at Yahoo has proven elusive for years now and Thompson's success growing PayPal into what should soon be eBay's largest business may not transfer over. Alibaba may also find Thompson as difficult to deal with as Bartz.

According to the Wall Street Journal, this summer "PayPal said it would stop providing electronic-payment services for AliExpress, an online sales platform run by Alibaba Group unit Alibaba.com Ltd. The termination came after Alibaba resisted a bid by PayPal to increase the rates it charged for services on the platform."

During Thompson's administration Yahoo said PayPal solidified its lead as the global online payment service, expanded its user base from 50 million to more than 104 million active users in 190 countries worldwide, increased the number of merchant partners to more than eight million globally, and grew revenues from $1.8 billion to upwards of $4 billion in 2011.

Forbes suggests that PayPal is headed for a spin-off and that Thompson is leaving a mint and a far easier job behind to join Yahoo.

Bostock, who claimed Yahoo wouldn't be going private on the conference call, said, "Scott brings to Yahoo a proven record of building on a solid foundation of existing assets and resources to reignite innovation and drive growth, precisely the formula we need at Yahoo."

Before running PayPal for four years he was its CTO and before that executive vice-president of technology solutions at Inovant, the unit formed to oversee Visa's global technology.

Thompson's departure leaves eBay in a lurch. eBay CEO John Donahoe, who only found out Thompson was leaving Tuesday afternoon, will step in as PayPal's president until a replacement can be found. eBay shares fell too.