Linux is available in many different distributions, and this is why the operating system appeals to a particular sub-set of computer users, who are typically well qualified to go through the more advanced options and tweak their settings for themselves. Linux distros are plentiful, and there are many more than just the well known variety. Ubuntu, Red Hat and Arch Linux are some names that most of us have heard of, though another option now exists.
As BBC News reported, a group of SourceForge users released what they call "Anonymous-OS". The 1.5GB download is based upon the Ubuntu distribution, with @AnonOps reporting it to be full of trojans and advising people to stay away from it, and anything it offered. The authors of the distro baked in tools for examining website security and other things which could be used for nefarious purposes, requesting people did not use it to destroy web pages.
Trend Micro's European security research director, Rik Ferguson, chose to install the operating system when it was available. He noted it to be a functional OS, with options simply added. Among these was the Tor client, for anonymous browsing. It shares some similarities with another existing Linux distribution called Back Track, so it is possible the creators were trying to follow in the footsteps of another client.
SourceForge have since taken down the Anonymous-OS project, with a lengthy explanation as to why. In typical Internet "TL:DR" fashion the final few paragraphs sum everything up. Different security experts examined the operating system, determined it to be a threat, and then acted upon it. Open-source software can only succeed with trust in the developer, and there isn't much to trust in an operating system which might not have been developed by members of Anonymous at all.