The committee's top Democrat, Sen. Max Baucus of Montana, and top Republican, Sen. Orrin Hatch of Utah, criticized Sebelius for not being more forthcoming about problems with developing the complex marketplace that services 36 states, including Utah.
Hatch said Sebelius' past assurances of a smooth implementation "were, at best, misinformed."
"I would have preferred that you and the rest of the administration were honest with us to begin with," he said, requesting that she make monthly visits to the committee to provide status updates on the health law.
Hatch, like many Republicans, warned that those who buy insurance on the new federal marketplace, when it is fully operational, may become the victims of identity theft, since detailed testing did not take place before the site launched, then crashed, on Oct. 1.
But Sebelius defended the security systems in place at healthcare.gov, saying they meet federal standards. She said the site doesn't ask for any health information and while it does ask for a Social Security number and income information, that data is only used to identify a person and is not stored.
"There are risks with every system that goes live and, we took those risks very seriously," she said.
A software tester in Arizona found anyone could reset applicants passwords and potentially take control of their account, a problem that Sebelius told a House hearing last week has been fixed.
She said such upgrades to the site are happening day and night, allowing the site to load faster and interact with other federal databases without delays. Sebelius reported the site can handle 17,000 registrants an hour, though she refused to answer Hatch's question about how many have actually signed up for insurance through the system.
The administration plans to release that number next week.
The site is designed to offer insurance to the uninsured and those who aren't covered through their jobs or a government program like Medicare. People in this group have until Dec. 15 to enroll if they want coverage on Jan. 1. The open enrollment period will last until the end of March. Anyone without insurance at that time will face a tax penalty.