Poloniex -- suddenly holding everyone's funds and locking accounts? SCAM.
AFAIK this incident happen when they comply with KYC/AML and lock every users which meet certain condition, but haven't verify KYC/AML.
But if that's enough to be qualified for your blacklist, then HitBTC definitely should be in the list since recently the lock many users after they introduced stricter KYC verification process and that also happen on past with different reason.