Poloniex

Poloniex is a US-based digital asset exchange offering maximum security and advanced trading features.=

The vast majority of customer deposits are stored offline in air-gapped cold storage. We only keep enough online to facilitate active trading, which greatly minimizes risk and exposure.

Their auditing programs monitor exchange activity 24/7/365. Their job is to report and block any suspicious activity before it becomes a problem.

Any funds you put into the exchange are only used to facilitate trading through your account. Unlike banks, we do not operate on fractional reserves.