I would assume the files are encrypted with a symmetric cipher like AES.
Known plaintext attacks are not very effective against symmetric ciphers.
Indeed they're designed to be resilient to chosen plaintext attacks.
More likely they registered that domain for brand protection and repurposed it to keep their services up while they regain control of the.com. It's easier to register a domain than go through the UDRP with ICANN and/or the applicable registry to take it down when someone starts using it maliciously.
The ACLU has done a lot for various freedoms, including internet freedoms. One instance, where the ACLU represented an ISP that was served with National Security Letters, serves to illustrate the kinds of high profile and essential litigation they perform.
Yeah, but they have contract terms that basically allow them to discontinue your service for any or no reason whatsoever, so it's not like that changes much. I suppose the only difference would be, in the case of breaches of contract, you wouldn't get a refund.