Taking on a new leader while the company continues to struggle will be a challenge. "The problem with a new CEO is if you have more of a revolving door," Sterling said. Often, new leaders want to bring in their trusted advisers and remove some existing executives.

In a statement, Bostock thanked Bartz for "her service to Yahoo! during a critical time of transition in the company's history, and against a very challenging macro-economic backdrop."

At the time of this report, Yahoo's shares were up more than 6 percent in after-hours trading, at $13.72.

The IDG News Service