This is Bitfinex's response:
Bitfinex and BitGo Partner to Create World’s First Real-Time Proof of Reserve Bitcoin Exchange
Posted: about 4 hours ago
We are very excited to unveil our new Bitcoin settlement system and security architecture that for the first time ever offers complete segregation of all customer bitcoins. Based on BitGo’s revolutionary multi-signature technology, we are now able to provide individual multi-signature wallets for each customer, allowing traders to verify funds on the Blockchain for complete transparency while retaining institutional-level security.
Starting today we will begin using unique sets of keys for each user, and will separate each user’s funds on the public blockchain. This powerful combination of BitGo’s multi-sig technology with our exchange mitigates most of the shared pool security risks while simultaneously enabling users to verify their individual holdings on the blockchain.
We will start migrating users' accounts to the BitGo system over the next couple days. We hope to have the full migration completed in less than a week.