Microsoft said on Tuesday the patches released to guard against the Meltdown and Spectre security threats slowed down some personal computers and servers, with systems running on older Intel processors seeing a noticeable decrease in performance.

The company expects most users with PCs made during or prior to 2015 running operating systems older than Windows 10 to notice a decrease in system 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.

Meltdown and Spectre are two memory access 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.