Folks at XDA forums may have found a vulnerability in WP8.1 that means it could be “jailbroken” or at least, as a redditor puts it, ‘unlatched’ ;p.
In terms of additional privileges, it means installation of apps without the store. Now some fear that since this is being highlighted that MS will quickly patch it. But as also pointed out, that’s the beauty of MS. Quickly will probably mean next year.
Although instructions are provided, you are warned not to do this. Only if you know what you’re doing and only then should you consider that your warranty will not be covered etc.