Microsoft has cut off access to dozens of its open source projects hosted on GitHub as it investigates how hackers apparently breached the projects and injected password-stealing malware into the code.

Many of the affected projects relate to Microsoft’s cloud service Azure and other tools used by developers to code with AI development apps, such as Claude Code, Gemini’s command line interface, and VS Code.

According to security firm Cloudsmith and community-driven malware analysis site OpenSourceMalware, which were some of the first to flag the hack, the malware allowed the hackers to steal the users’ passwords and other sensitive credentials when they opened the compromised tools in their AI coding apps.

It’s not immediately known how many people have downloaded the affected tools.

Microsoft confirmed it pulled the repos, as first reported by 404 Media.

Microsoft spokesperson Ben Hope told TechCrunch that the company has “temporarily removed some repositories as we investigated potential malicious content.”

“Some of these repos have been restored after review, while others may remain offline while work continues.”

“As part of our investigation, we notified a small number of customers who may have pulled down content from the affected repositories. We will continue to investigate, and if anything further is identified that requires customer action, we will reach out directly through our established support channels,” added Hope.

Microsoft did not immediately provide the specific number of customers affected, when asked by TechCrunch.

At least 70 projects belonging to Microsoft have been “disabled,” per a message loading when trying to access the projects’ pages on GitHub, a code-hosting site that Microsoft owns. “Access to this repository has been disabled by GitHub Staff due to a violation of GitHub’s terms of service.”

This is the latest example in recent months of hackers breaching widely popular open source projects with the aim of planting malware on a large number of users who have the code installed on their computers. These hacks are known as “supply chain” attacks as they target code that is often used in a large number of software products, or by a specific kind of user, which may be advantageous to hack as they sometimes have access to cloud systems and large amounts of customers’ data.

While it’s not uncommon for sole developers of open source projects to be targeted by hackers — in some cases as part of long-running efforts to gain the trust of the developer — it is rare for large tech giants like Microsoft, which have the resources to defend against these kinds of attacks, to get breached.

This is Microsoft’s second known breach over the past few weeks that has allowed hackers to compromise its open source projects, per Ars Technica. In mid-May, security researchers said that Microsoft’s open source project Durable Task, a tool that helps developers build apps, was hacked. OpenSourceMalware said that Microsoft’s latest incident is a “re-compromise” of the Durable Task project, suggesting that Microsoft may not have eradicated the hackers on its first attempt or an entirely new, distinct breach.

Updated with comment from Microsoft.