Top quality drama going on. And not exactly surprising, either - "hey, lets all put 100m USD solely in the hands of an immutable blob of complex imperative code". I'm pretty stumped as to how $100m got into the fund, but maybe it's only worth that much due to value fluctuations in this cryptocurrency (which are presumably cratering right now).
If you're curious (I recommend it), I found these links pretty good to get the gist:
What is the DAO: http://www.coindesk.com/the-dao-just-raised-50-million-but-what-is-it/
As for ETH itself, it's a "smart contract" platform - where instead of having contracts interpreted by lawyers, they are written in code that lives forever in a bitcoin-like blockchain (i.e. the code is law for all who choose to participate, with no reliance on human interpretation). Here's a simple example to give you the gist: https://solidity.readthedocs.io/en/latest/introduction-to-smart-contracts.html#a-simple-smart-contract
The attacker's public response (probably fake, but it makes a fun point): http://pastebin.com/CcGUBgDG
And a choice quote from a month ago (https://news.ycombinator.com/item?id=11728592):
> Smart contracts should be thought of as "the Underhanded C Contest on the blockchain."