Intel Corp. did not inform U.S. cyber security officials of the so-called Meltdown and Spectre chip security flaws until they leaked to the public, six months after Alphabet Inc. notified the chipmaker of the problems, according to letters sent by tech companies to lawmakers on Thursday.

Current and former U.S. government officials have raised concerns that the government was not informed of the flaws before they became public because the flaws potentially held national security implications. Intel said it did not think the flaws needed to be shared with U.S. authorities as hackers had not exploited the vulnerabilities.

Intel did not tell the United States Computer Emergency Readiness Team, better known as US-CERT, about Meltdown and Spectre until Jan. 3, after reports on them in online technology site The Register had begun to circulate.

US-CERT, which issues warnings about cyber security problems to the public and private sector, did not respond to a request for comment.

Details of when the chip flaws were disclosed were detailed in letters sent by Intel, Alphabet and Apple Inc on Thursday in response to questions from Representative Greg Walden, an Oregon Republican who chairs the House Energy and Commerce Committee. The letters were seen by Reuters.

Alphabet said that security researchers at its Google Project Zero informed chipmakers Intel, Advanced Micro Devices Inc and SoftBank Group Corp-owned ARM Holdings of the problems in June.

It gave the chipmakers 90 days to fix the issues before public disclosing them, standard practice in the cyber security industry intended to give the targets of bugs time to fix them before hackers can take advantage of the flaws.

Alphabet said it left the decision of whether to inform government officials of the security flaws up to the chipmakers, which is its standard practice.

Intel said it did not inform government officials because there was "no indication that any of these vulnerabilities had been exploited by malicious actors," according to its letter.

Intel also said it did not perform an analysis of whether the flaws might harm critical infrastructure because it did not think it could affect industrial control systems. But Intel said that it did inform other technology companies that use its chips of the issue, according to its letter.

Intel, Alphabet and Apple could not immediately be reached for comment.

AMD, ARM, Microsoft Corp and Amazon.com Inc also responded to questions from lawmakers.

Microsoft said that it did inform several antivirus software makers about the flaws "several weeks" ahead of their public disclosure to give them time to avoid compatibility issues. AMD said that Alphabet extended the disclosure deadline from the standard 90 days twice, first to Jan. 3, then to Jan. 9.