Here’s a technical explanation from a Linux Weekly News contributor on the 2003 Linux Kernel hack.
An attempt to backdoor the kernel
[Posted November 6, 2003 by corbet]
The mainline 2.4 and 2.6.0-test kernels are both currently maintained in BitKeeper repositories. As a service for those who, for whatever reason, are unable or unwilling to use BitKeeper, however, the folks at BitMover have set up a separate CVS repository. That repository contains the current code and the full revision history. It is not, however, the place where new changes are committed. So, when somebody managed to push some changes directly into CVS, Larry McVoy noticed quickly.
Over the years, people have had numerous things to say about BitKeeper and the people behind it. Nobody, however, has accused them of being insufficiently careful. Every change in the CVS repository includes backlink information tying it to the equivalent BitKeeper changesets. The changes in question lacked that information, and thus stood out immediately.
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