Sony's recent run of legal and now technical issues with hackers can be traced back to a single decision: that of removing the ability to run the Linux operating system on the PlayStation 3. While Sony cut Linux out of piracy fears, fans were upset that it brought to an end over a decade of custom tinkering and homebrew development on PlayStation consoles.
All of which, it should be pointed out, was not just supported by Sony, but sold and endorsed by the company as well.
In 1997, Sony released a package called Net Yaroze. As amazing as this seems given the company's stance today, Net Yaroze was a homebrew development kit for the PS1, which let the man on the street (via mail order) get hold of a debug PlayStation console and all the necessary software they'd need to write their own PlayStation games.
The Net Yaroze bundle cost $750, and included not just a badass black matte console, but two controllers, software and all kinds of professional documentation bedroom coders would need to make their own games. The console was even region-free! About the only thing the package didn't include was the computer you needed to actually write the code on.
Sounds awesome, right? Well, there were catches. It wasn't a fully-fledged development suite, with serious limitations on the size of games that could be developed, meaning most home-baked games came out looking more like bad PC titles from the late 80s than quality PS1 games. It also came about too soon for the age of the internet, meaning actually sharing the games you'd created was almost impossible.
Because of this, the Net Yaroze only lasted a few years. While there was never a Net Yaroze 2, in 2002 Sony went one better and released Linux for PlayStation 2.
As the program's title implies, this was a Linux development kit for the PlayStation 2, which not only allowed users to create their own software but, being a fully-fledged operating system, could turn their console into a computer. While this led to a spate of emulators popping up for the PS2, running everything from old NES games to...old SNES games, people did take the time to create homebrew PS2 games, which by virtue of its later release meant that, unlike Net Yaroze, these games could be distributed online. It could also run things like X Window.
Linux for PlayStation 2 still suffered from other problems it shared with Net Yaroze, however, like size restrictions and an inability to code games which made use of the console's DVD drive. Another problem was that in order to play games made using Linux for PlayStation 2, another user had to have Linux for PlayStation 2 installed on their own console, which given the level of technical experience required and scarcity of copies available (the program was only around for a couple of years) meant barely anybody would get the chance to check the games out.
On the bright side? It came with a pretty cool PS2-branded keyboard and mouse.
The love affair with Linux continued when the PlayStation 3 launched in 2006, as the "other OS" feature included with the console allowed users to install Linux on their consoles, once again allowing people the option of turning their games machine into a computer. Yet amid growing concerns this was creating loopholes for attempts at hacking the console, Sony removed the feature, first from the PS3 Slim (released in 2009) and then all older models with a firmware update in 2010.
So as you can see, when Sony ended support for Linux, it wasn't just canning a niche PS3 feature. It was bringing to an end 13 years of support for users doing cool, custom things with their PlayStation consoles. While this doesn't excuse the militant actions of hackers that have brought about the current PSN downtime, this at least gives you an idea of why that particular community was so upset at the loss of Linux from the PS3.