In order to get access to any Bitcoin wallet you need a private key. But if you try to brute it, you’d need the amount of time from Big Bang to now for 15-digit password, but private key have 52 digits. That’s why it’s impossible to hack this way. But attackers had found the way to steal more that 1800 BTC!

Brain wallet

There is the way to get you password on bitaddress.org with «brain wallet». You use your own any password to generate a private and open keys.

How I found private keys

As we know, It’s impossible to find private key, but it’s possible to find this personal "brain" key, because people often use light vulnerable keys using just few symbols, names, lyrics, phrases and proverbs.

I found existing wallet with money but coins had withdrawn earlier. I Just tried the dumbest things people could've done: first of all I wrote all the letters on my keyboard. And it WORKED OUT! :)
Password is all the letters of keyboard(as on the previous gif). It was 1 BTC on the generated address:

I was very excited and moved on trying to come across a fortune. I used address of Bitadress.org creator as "brain password":

I've found about 5 more existing wallets with money! But unfortunately coins was withdrew from all found wallets about year or two ago.

Then I tried to use as my «brain key» just text parts of the main page of the same site:

I searched for such cases in internet and found interesting articles.

Attackers stole 1,806 BTC from brain wallets

I've found here and here that most bitcoin brain wallets drained by attackers. They used programs which brute all the words from all the dictionaries, all languages, phrases, names, numbers, song lyrics, some books phrases, aphorisms etc.
More than 1000 brain wallets was drained by criminals, they stole more than $103,000, about 1,806 BTC. Nowadays it would cost about $2,000,000.

So, be careful using brain wallet, your brain is not so safe as SHA256 encrypting. :)
And be sure that your thoughts are much more easier than cryptographic fifty-digit password!
Despite our external differences, we're pretty similar internal that makes us vulnerable and very predictable. Know yourself in order to know all the people. :)

And finally stop using your birthday as pin code and names of you and your lover as your passwords.

So, how much bitcoins would you like to find? And what would you do with the buried treasure? ;)