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Funds should be kept in whatever places you prefer, where you are in 100% control of your private keys. It can be hardware wallets, paper wallets, even hot wallets on a dedicated smartphones (for small amounts).
Exchanges are OK if you like to change from one coin to another. As soon as you done this - run away from the exchange. Do not keep your funds there even for one extra hour.

One may reply - what about trading?
Well, trading is mainly driven by one thing, by greed, by one single desire - to have more.
Yes, there is a possibility to have more (by trading).
As with every possibility to profit - here comes risks.
Big profit possibilities brings big, HUGE risks.
There is hardly any other more risky place to keep our cryptos than on centralized exchanges.
Who said this (Andreas?) - there are only two types of exchanges :
Those which already been hacked, and those which WILL BE hacked.

Below is a nice short list of 10 famous crypto places:
PicoStocks, Mt.Gox, BTC-E, Poloniex, Bitcurex, Cryptsy, BTER, MintPal, Bitstamp, ShapeShift

Guess what three common hings I can say about them?

  1. I had accounts, and been used them one time or another there, in all 10 of them
  2. All 10 been hacked in the past, and lost their client funds
  3. I have never lost even one single satoshi in any of those 10 places

Why?
Because I do not trade, at least not day trading. And I REMOVE my funds immediately once I have my desired exchange completed.

Seems like a simple rule?
But it works !