Yahoo!, the Web portal that revamped its e-mail service in October, apologized for a “hardware problem” that has knocked out access to the service for some users since Dec. 9.

The company has “dozens of people working around the clock to bring it to a resolution,” and expects access to be restored by 3 p.m. San Francisco time today, Jeffrey Bonforte, a senior vice president at Yahoo, said on the company’s website.

“The issue has been harder to fix than we originally expected,” Bonforte wrote.

The outage adds to the troubles that have beset the e-mail platform -- used by more than 100 million people daily -- since Chief Executive Officer Marissa Mayer redesigned the service. Users have complained about software issues as well as the look and organization of the new mail site, including searches for older messages and new characteristics, like conversation threads, that mirror Google’s rival Gmail service.

Bloomberg News