Sony appears to be using copyright law in an attempt to remove all traces of a leaked PlayStation 4 Software Development Kit (PS4 SDK) from the Web. That effort also seems to have extended in recent days to the forced removal of the mere discussion of the leak and the posting of a separate open source, homebrew SDK designed to be used on jailbroken systems.
The story began a few weeks ago, when word first hit that version 4.5 of the PS4 SDK had been leaked online by a hacker going by the handle Kromemods. These SDKs are usually provided only to authorized PS4 developers inside development kits. The SDKs contain significant documentation that, once made public, can aid hackers in figuring out how to jailbreak consoles, create and install homebrew software, and enable other activities usually prohibited by the hardware maker (as we've seen in the wake of previous leaks of PlayStation 3 SDKs).
While you can still find reference to the version 4.5 SDK leak on places like Reddit and MaxConsole, threads discussing and linking to those leaked files on sites like GBATemp and PSXhax, for example, appear to have been removed after the fact. Cachedversions of those pages show links (now defunct) to download those leaked files, along with a message from KromeMods to "Please spread this as much as possible since links will be taken down... We will get nowhere if everything keeps private; money isn't everything."