Bitcoin is very safe, but there have been many thefts (and will continue to be, it is inevitable) of hundreds of millions of dollars, even, in BTC. But one thing does not take away the other, and that is what we are going to explain.
In exchange houses lies the problem of Bitcoin security
And here we draw two factors in which security can fail: the end user (the owner of the Bitcoin) and the exchange house. Both are people and, therefore, can fail. On the side of the exchange house, there are also other risks: it can have a security hole, allowing a hacker to have access to the keys, or it can even simulate a theft (which would be an autorobo).
On the user's side, this can be hacked (as if they hacked into Facebook). In fact, it is relatively simple: through an unsafe password (or a password shared with other accounts, for example, social networks, and that has been exposed in some other hacking), through a phishing attack or even through a simple keylogger .
The most common, however, when they steal large amounts of Bitcoin, is to steal an exchange house, because from there we can access the Bitcoin not only one person, but millions. The thefts to private individuals, on the other hand, are less frequent, because, as they can have millions in Bitcoin, they can also have just a few cents.
It's like comparing stealing a bank with stealing wallets by the meter (in the wallets there can be an interesting sum or nothing, in the bank, if you manage to violate their security, you have a lot of money).
