steemit.com is attackable, but the blockchain is virtually impervious (at this moment). Probably has something to do with Steem making it to the news the last week, and on Wired.com this past Wednesday. Here's another post that talks about the blockchain being unaffected: https://steemit.com/witness-category/@dragosroua/steemit-com-is-under-a-ddos-attack-but-the-steem-blockchain-is-ok