The Linux Foundation and related websites have been taken down following a compromise discovered on 8 September.
The websites were taken offline "in the interest of extreme caution and security best practices," the Linux Foundation said on a holding page.
"We are in the process of restoring services in a secure manner as quickly as possible," the organisation said.
"As with any intrusion and as a matter of caution, you should consider the passwords and SSH [Secure Shell] keys that you have used on these sites compromised. If you have reused these passwords on other sites, please change them immediately."
The foundation said it was auditing all systems and will update the statement once more information emerges.
"The Linux Foundation infrastructure houses a variety of services and programs including Linux.com, Open Printing, Linux Mark, Linux Foundation events and others, but does not include the Linux kernel or its code repositories," it added.
The body said it believes the breach on LinuxFoundation.org was related to an intrusion on Kernel.org discovered last month.
We currently believe that the source code repositories were unaffected.
The Kernel.org website currently says it is down for maintenance. In August, a number of servers in the Kernel.org infrastructure were hacked.
"While we currently believe that the source code repositories were unaffected, we are in the process of verifying this and taking steps to enhance security across the kernel.org infrastructure," a note previously on Kernel.org read.
According to the Hacker News, the Phalanx rootkit was used to eventually gain root access to Kernel.org systems.
Authorities in both the US and Europe have been notified.
