Update:
A few hours after my post, the store opened again, and the method to get the apps outside the "walled garden" is still working.
So it looks like it was a coincidence - real planned maintenance a few hours after a security issue.
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On the CrackBerry forums xsacha opened uo the floodgates by releasing a way to download any app from the BlackBerry store on a PC, for "backup" or other less legit reasons.
A few hours laters, every BlackBerry in the world can't access anymore to the store, for planned maintenance.
Yeah... "planned"