The two cases are different and the truth about what really happened will take years to be made public. We talk about fraud, theft by employees, hacker attack, mismanagement, money laundering, etc.
In both cases, the sites had a respectable appearance before D-Day but customers around the world, like you and me, who had currencies or bitcoins stored on these platforms lost a significant portion of their assets [between 55 and 100%] ... And to recover the rest, the procedures will last for years.
All exchanges are private companies which are, to date, subject to very few regulations. In addition, the assets that you entrust to them do not benefit from any guarantee of the state or other, as it is often the case for your bank accounts.
How to protect yourself ?
First of all, it is prudent to take a serious look at society and the people behind it.
For example, Bitstamp and Coinbase have voluntarily applied for licenses in Europe and the United States respectively. It is rather a good indicator of seriousness. But it's not generalized ...
Then, what to think of a site that has technical problems repeatedly? Is the technical team up against piracy? (Yes Kraken, I look to you!)
Even worse, some exchanges, especially in the Altcoins category, completely hide their identity (eg: hitBTC). What trust can we have in an exchange whose owners are hiding even before there has been any problem?
I will come back to you on the questionable exchanges. Waiting:
Prudential strategy "all terrain"
Whatever the level of seriousness, an exchange is never 100% safe from a hacker attack very well organized and it can be fatal. We have seen recently a security vulnerability within all intel micro-processors sold since 1996! This flaw affects web servers around the world that run on intel processors.
How could an exchange, however serious, protect against this?
We want to say that they could not ... but in fact if ... and the serious ones do it: they store 80% of the bitcoins that were entrusted to them offline, that is to say: in a wallet that is not connected to the internet.
But you, you can not know what your exchanges really do ...
So the best practice is not to leave a significant part of your funds and your corners on the exchanges. The best practice is to repatriate your corners in a safe (electronic) offline and under your control: a hardware wallet (digital wallet).