Re: Is there any danger /risk having my bitcoins at Poloniex,Bitrex after 1 August ?
Is there any danger / risk having my bitcoins at poloniex after 1. August ? Also will my current Bitcoins remain Bitcoins (and not BCCs or a mix) at poloniex and bittrex after 1. August ? Cant find the answer anywhere ! 
Statement by Poloniex
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We will be disabling deposits and withdrawals of Bitcoin (and all BTC related tokens) any time we deem necessary to ensure that all tokens stored on Poloniex remain safe. The length of any possible downtime is unknown as this is highly dependent on network stability.
At this time, we cannot commit to supporting any specific blockchain that may emerge if there is a blockchain split. Even if two viable blockchains emerge, we may or may not support both and will make such a decision only after we are satisfied that we can safely support either blockchain in an enterprise environment.
If you don't want to leave the decision of which Bitcoin tokens to support (or recognize as valid) to a 3rd party, you should not keep your tokens on any 3rd party platform.
At this time, we cannot commit to supporting any specific blockchain that may emerge if there is a blockchain split. Even if two viable blockchains emerge, we may or may not support both and will make such a decision only after we are satisfied that we can safely support either blockchain in an enterprise environment.
If you don't want to leave the decision of which Bitcoin tokens to support (or recognize as valid) to a 3rd party, you should not keep your tokens on any 3rd party platform.
https://poloniex.com/press-releases/2017.07.24-Our-plans-to-handle-potential-BTC-network-disruptions/
Statement by Bittrex
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Bittrex will close deposits and withdrawals of Bitcoin (including 2nd layer protocol XCP/OMNI and associated assets) 24 hours prior to the BCC UAHF time on August 1st, 5:20am (12:20pm UTC). The wallet will remain closed until the majority hash power chain is clearly established.
Bittrex will monitor the BCC network and developments and assess the viability of opening trading of BCC assets. There is no guarantee that any markets will open to allow BCC assets to be tradable on Bittrex exchange.
Bittrex will monitor the BCC network and developments and assess the viability of opening trading of BCC assets. There is no guarantee that any markets will open to allow BCC assets to be tradable on Bittrex exchange.
https://support.bittrex.com/hc/en-us/articles/115000808991-Statement-on-Bitcoin-Cash-BCC-?mobile_site=true
Poloniex and Bittrex currently have no plans to add BCC. Obviously all exchanges would temporarily suspend their operations on August 1. Is your bitcoin safe in Poloniex or other exchanges? It is as safe as keeping your bitcoins on a third party website with no access to private keys. You should move your funds to where you have access to private keys.