On Good Friday, a Microsoft engineer named Andres Freund noticed something peculiar. He was using a software tool called SSH for securely logging into remote computers on the internet, but the interactions with the distant machines were significantly slower than usual. So he did some digging and found malicious code embedded in a software package called XZ Utils that was running on his machine. This is a critical utility for compressing (and decompressing) data running on the Linux operating system, the OS that powers the vast majority of publicly accessible internet servers across the world. Which means that every such machine is running XZ Utils.

Freund’s digging revealed that the malicious code had arrived in his machine via two recent updates to XZ Utils, and he alerted the Open Source Security list to reveal that those updates were the result of someone intentionally planting a backdoor in the compression software. It was what is called a “supply-chain attack” (like the catastrophic SolarWinds one of 2020) – where malicious software is not directly injected into targeted machines, but distributed by infecting the regular software updates to which all computer users are wearily accustomed. If you want to get malware out there, infecting the supply chain is........

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