The White House, the NSA and the Office of the Director of National Intelligence issued statements after Bloomberg reported that the NSA was aware of the bug for at least two years and exploited it in order to obtain passwords and other basic information used in hacking operations. The Bloomberg report cited two unnamed sources it said were familiar with the matter.
The Heartbleed bug is considered one of the most serious Internet security flaws to be uncovered in recent years.
(Also see: Heartbleed bug: What you need to know)
"Reports that NSA or any other part of the government were aware of the so-called Heartbleed vulnerability before April 2014 are wrong," White House National Security Council spokeswoman Caitlin Hayden said in a statement.
"This administration takes seriously its responsibility to help maintain an open, interoperable, secure and reliable Internet," Hayden added.
Bloomberg was not immediately available to comment.
The discovery of Heartbleed by researchers with Google Inc and a small security firm, Codenomicon, prompted the U.S. Homeland Security Department to advise businesses on Tuesday to review their servers to see if they were using vulnerable versions of widely used software known as OpenSSL.
OpenSSL is used to encrypt email and other communications and to protect the websites of big Internet companies, including Facebook Inc, Google Inc and Yahoo Inc. The bug, disclosed Monday, allows hackers to steal data without a trace.
(Also see: Gmail, Facebook, Twitter, Yahoo, others: What passwords to change in Heartbleed aftermath?)
NSA spokeswoman Vanee Vines said in a separate statement: "NSA was not aware of the recently identified vulnerability in OpenSSL, the so-called Heartbleed vulnerability, until it was made public in a private-sector cybe-rsecurity report."
Hayden said the federal government relies on OpenSSL to protect the privacy of users of government websites and other online services. "If the federal government, including the intelligence community, had discovered this vulnerability prior to last week, it would have been disclosed to the community responsible for OpenSSL," Hayden added.
Hayden said that when U.S. agencies discover a new vulnerability in commercial and open-source software, "it is in the national interest to responsibly disclose the vulnerability rather than to hold it for an investigative or intelligence purpose." Such vulnerabilities are known as "zero-day" flaws because the software developers have had zero days to fix them.
(Also see: 'Heartbleed' computer bug threat spreads to firewalls and beyond)
In December, a five-member advisory panel convened to review electronic surveillance policy urged the White House to sharply curtail the use of undisclosed flaws and stop undercutting encryption standards. The panel included former White House cyber-security advisor Richard Clarke.
In late February, a senior White House official said the Obama administration was intensively studying both issues.
The administration statements issued on Friday confirmed that the review had already "reinvigorated an interagency process for deciding when to share vulnerabilities" on a case-by-case basis.
The activities of the NSA have come under sharp scrutiny since former agency contractor Edward Snowden leaked numerous documents exposing expansive U.S. surveillance efforts.
Even before Snowden's emergence, former officials, including Clarke, told Reuters that offensive and spying considerations had dominated inside the NSA, causing it to withhold information instead of warning the public about new flaws.
Clarke told Reuters Friday that the NSA had not known of Heartbleed.
The U.S. government warned banks and other businesses on Friday to be on alert for hackers seeking to steal data exposed by the bug, as a German programmer who volunteered with OpenSSL took responsibility for inadvertently launching the security crisis.
© Thomson Reuters 2014
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