(Rewrites throughout with comments from Microsoft blog post)
FRANKFURT, Jan 9 (Reuters) - Microsoft Corp said on Tuesday the patches released to guard against Meltdown and Spectre security threats slowed down some personal computers and servers, with systems running on older Intel Corp processors seeing a noticeable decrease in performance.
The security updates also froze some computers running AMD chipsets, Microsoft said in a blog post, citing customer complaints.
"We (and others in the industry) had learned of this vulnerability under nondisclosure agreement several months ago and immediately began developing engineering mitigations and updating our cloud infrastructure," Microsoft executive Terry Myerson wrote in a blog. (http://bit.ly/2mj6f3Q)
Meltdown and Spectre are two memory corruption flaws that could allow hackers to bypass operating systems and other security software to steal passwords or encryption keys on most types of computers, phones and cloud-based servers.
Intel said last week that fixes for security issues in its microchips would not slow down computers, rebuffing concerns that the flaws would significantly reduce performance.
Rival AMD had also played down the threat, saying its products were at "zero risk" from the Meltdown flaw, but that one variant of the Spectre bug could be resolved by software updates from vendors such as Microsoft.
AMD and Intel were not immediately available for further comment. (Reporting by Eric Auchard in Frankfurt and Supantha Mukherjee in Bengaluru; Editing by Edmund Blair, Mark Potter and Saumyadeb Chakrabarty)