WASHINGTON -- WASHINGTON (AP) — Defending President Barack Obama's much-maligned health care overhaul in Congress, his top health official was confronted Wednesday with a government memo raising new security concerns about the trouble-prone website that consumers are using to enroll.

The document, obtained by The Associated Press, shows that administration officials at the Centers for Medicare and Medicaid Services were concerned that a lack of testing posed a potentially "high" security risk for the HealthCare.gov website serving 36 states. It was granted a temporary security certificate so it could operate.

Security issues are a new concern for the troubled HealthCare.gov website. If they cannot be resolved, they could prove to be more serious than the long list of technical problems the administration is trying to address.

"You accepted a risk on behalf of every user...that put their personal financial information at risk," Rep. Mike Rogers, R-Mich., told Health and Human Services Secretary Kathleen Sebelius during questioning before the House Energy and Commerce Committee. "Amazon would never do this. ProFlowers would never do this. Kayak would never do this. This is completely an unacceptable level of security."

Sebelius countered that the system is secure, even though the site has a temporary certificate, known in government parlance as an "authority to operate." Sebelius said a permanent certificate will only be issued once all security issues are addressed.

Added spokeswoman Joanne Peters: "When consumers fill out their online...applications, they can trust that the information they're providing is protected by stringent security standards and that the technology underlying the application process has been tested and is secure. Security testing happens on an ongoing basis using industry best practices."

A security certificate is required before any government computer system can process, store or transmit agency data. Temporary certificates are allowable, but under specific circumstances.

Earlier, the secretary said she's responsible for the "debacle" of cascading problems that overwhelmed the government website intended to make shopping for health insurance clear and simple.

"Hold me accountable for the debacle," Sebelius said during a contentious hearing. "I'm responsible."

Sebelius is promising to have the problems fixed by Nov. 30, even as Republicans opposed to Obama's health care law are calling in chorus for her resignation. She told the committee that the technical issues that led to frozen screens and error messages are being cleared up on a daily basis.

Addressing consumers, Sebelius added, "So let me say directly to these Americans, you deserve better. I apologize."

The Sept. 27 memo to Medicare chief Marylin Tavenner said a website contractor wasn't able to test all the security controls in one complete version of the system.

"From a security perspective, the aspects of the system that were not tested due to the ongoing development, exposed a level of uncertainty that can be deemed as a high risk for the (website)," the memo said.

It recommended setting up a security team to address risks, conduct daily tests, and a full security test within two to three months of going live.

HealthCare.gov was intended to be the online gateway to coverage for millions of uninsured Americans, as well those who purchase their policies individually. Many people in the latter group will have to get new insurance next year, because their policies do not meet the standards of the new law.

Sebelius' forthright statement about her ultimate accountability came as she was being peppered with questions by Rep. Marsha Blackburn, R-Tenn., about who was responsible. It was Blackburn who introduced the term "debacle."

Rep. Henry Waxman of California, the ranking Democrat on the committee, scoffed at Republican "oversight" of a law they have repeatedly tried to repeal.

"I would urge my colleagues to stop hyperventilating," said Waxman. "The problems with HealthCare.gov are unfortunate and we should investigate them, but they will be fixed. And then every American will have -- finally have access to affordable health insurance."

Throughout the hearing, Sebelius was respectful and poised, often addressing lawmakers as "sir" or "congresswoman." She kept her cool as some lawmakers repeatedly cut off her answers. But she did not shy a few times from tersely interjecting her views while a member was speaking.

The standing-room-only hearing room was silent when she swore an oath to tell the truth and began her statement. "I apologize," she told the rapt committee.

Sebelius faced questions about problems with the website as well as a wave of cancellation notices hitting individuals and small businesses who buy their own insurance.

Lawmakers also want to know how many people have enrolled in plans through the health exchanges, a number the Obama administration has so far refused to divulge, instead promising to release it in mid-November.

On Tuesday, Medicare chief Marilyn Tavenner was questioned for nearly three hours by members of the House Ways and Means Committee who wanted to know why so many of their constituents were getting cancellation notices from their insurance companies.

The cancellations problem goes to one of Obama's earliest promises about the health law: You can keep your plan if you like it. The promise dates back to June 2009, when Congress was starting to grapple with overhauling the health care system to cover uninsured Americans.

As early as last spring, state insurance commissioners started giving insurers the option of canceling existing individual plans for 2014, because the coverage required under Obama's law is significantly more robust. Some states directed insurers to issue cancellations. Large employer plans that cover most workers and their families are unlikely to be affected.

The law includes a complicated "grandfathering" system to try to make good on Obama's pledge. It shields plans from the law's requirements provided the plans themselves change very little. Insurers say it has proven impractical. The cancellation notices are now reaching policyholders.

Tavenner blamed insurance companies for cancelling the policies and said most people who lose coverage will be able to find better replacement plans in the health insurance exchanges, in some cases for less money.

Also on HuffPost:

Loading Slideshow...
  • 1912

    Former President Theodore Roosevelt champions national health insurance as he unsuccessfully tries to ride his progressive Bull Moose Party back to the White House. (Photo by Topical Press Agency/Getty Images)

  • 1935

    President Franklin D. Roosevelt favors creating national health insurance amid the Great Depression but decides to push for Social Security first. (Photo by Keystone/Getty Images)

  • 1942

    Roosevelt establishes wage and price controls during World War II. Businesses can't attract workers with higher pay so they compete through added benefits, including health insurance, which grows into a workplace perk. (Photo by Hulton Archive/Getty Images)

  • 1945

    President Harry Truman calls on Congress to create a national insurance program for those who pay voluntary fees. The American Medical Association denounces the idea as "socialized medicine" and it goes nowhere. (Photo by Keystone/Getty Images)

  • 1960

    John F. Kennedy makes health care a major campaign issue but as president can't get a plan for the elderly through Congress. (Photo by Keystone/Getty Images)

  • 1965

    President Lyndon B. Johnson's legendary arm-twisting and a Congress dominated by his fellow Democrats lead to creation of two landmark government health programs: Medicare for the elderly and Medicaid for the poor. (AFP/AFP/Getty Images)

  • 1974

    President Richard Nixon wants to require employers to cover their workers and create federal subsidies to help everyone else buy private insurance. The Watergate scandal intervenes. (Photo by Keystone/Getty Images)

  • 1976

    President Jimmy Carter pushes a mandatory national health plan, but economic recession helps push it aside. (Photo by Central Press/Getty Images)

  • 1986

    President Ronald Reagan signs COBRA, a requirement that employers let former workers stay on the company health plan for 18 months after leaving a job, with workers bearing the cost. (MIKE SARGENT/AFP/Getty Images)

  • 1988

    Congress expands Medicare by adding a prescription drug benefit and catastrophic care coverage. It doesn't last long. Barraged by protests from older Americans upset about paying a tax to finance the additional coverage, Congress repeals the law the next year. (TIM SLOAN/AFP/Getty Images)

  • 1993

    President Bill Clinton puts first lady Hillary Rodham Clinton in charge of developing what becomes a 1,300-page plan for universal coverage. It requires businesses to cover their workers and mandates that everyone have health insurance. The plan meets Republican opposition, divides Democrats and comes under a firestorm of lobbying from businesses and the health care industry. It dies in the Senate. (PAUL J. RICHARDS/AFP/Getty Images)

  • 1997

    Clinton signs bipartisan legislation creating a state-federal program to provide coverage for millions of children in families of modest means whose incomes are too high to qualify for Medicaid. (JAMAL A. WILSON/AFP/Getty Images)

  • 2003

    President George W. Bush persuades Congress to add prescription drug coverage to Medicare in a major expansion of the program for older people. (STEPHEN JAFFE/AFP/Getty Images)

  • 2008

    Hillary Rodham Clinton promotes a sweeping health care plan in her bid for the Democratic presidential nomination. She loses to Obama, who has a less comprehensive plan. (PAUL RICHARDS/AFP/Getty Images)

  • 2009

    President Barack Obama and the Democratic-controlled Congress spend an intense year ironing out legislation to require most companies to cover their workers; mandate that everyone have coverage or pay a fine; require insurance companies to accept all comers, regardless of any pre-existing conditions; and assist people who can't afford insurance. (Alex Wong/Getty Images)

  • 2010

    With no Republican support, Congress passes the measure, designed to extend health care coverage to more than 30 million uninsured people. Republican opponents scorned the law as "Obamacare." (Mark Wilson/Getty Images)

  • 2012

    On a campaign tour in the Midwest, Obama himself embraces the term "Obamacare" and says the law shows "I do care." (BRENDAN SMIALOWSKI/AFP/Getty Images)