Let me start by saying, very sorry for you loss mate. Yes I've been hearing about this possibility for quite some time now and yes, exchanges and online webwallets could without a doubt get hacked. Keeping your funds on these exchanges is a daily risk. It's not just poloniex were talking about here. Could be bittrex, kraken, etc. But let me ask you... do you use the 2FA code before signing in? Do you open an incognito tab while using poloniex? I've been advising people to get a hardware wallet such as the ledger nano s to keep your bitcoins and altcoins secure, that way yours funds are secure and away from prying eyes.

I personally don't keep anything on an exchange unless I wanna trade. Again, sorry for your loss. My advise to you is don't give up, see this as a learning experience and move on. If you wanna learn how to keep your bitcoin and altcoins secure, follow me!