Since the top brass at EA were dumb enough to go through with the hated and repined always-on DRM, there were consequences to be had. SimCity has been a disaster in the media circles since launch all because of the DRM, and now things have gone to the next level as a hack has been discovered that lets anyone invade any of the online cities and lay waste to them...permanently.
CVG noted that EA's director of communications, Erik Reynolds, has been transparent about removing all talk about hacks on the official EA forums due to their terms of service, as noted in Reynolds' tweet.
As a quick recap: Modders found out that you can play SimCity in offline mode as a single-player game. In addition to playing the game offline, the modders have also opened up additional things like larger cities, expanded highways and better population management. In other words, they fixed the broken game that EA shoved down your throats.
However, with all this good news also comes some bad news. Modders have also discovered that it's possible to mess with files client-side to affect server-side activity. I think you all know where this is going.
Basically, as the video shows below, you can enter into another person's online town and wreak havoc, however the modder notes that he turned off synching to the server so as not to actually cause permanent harm to his friend's city.
It's still awesome because this hack is only as destructive as it is because of EA's decision to make the game always-on. If the game hadn't had always-on DRM then this hack wouldn't be half as devastating as it is. Having EA delete these kind of topics from their forums is great damage control but don't be surprised if there's another furor when people start raging on the forums when some hacker decides to go through and Godzilla everyone's town. Enjoy.