In August 2010, someone broke Bitcoin itself, and almost nobody was awake to see it.

On August 15, a developer named Jeff Garzik opened a thread on the Bitcoin forum with a title that sounds boring today: "Strange block 74638."
Inside that block sat a single transaction that had created 184,467,440,737 bitcoins out of nothing.
To understand how insane that is, remember that Bitcoin is supposed to have a hard limit of 21 million coins, forever.
At that moment only about 3.8 million existed. One person had just printed almost 8,800 times the entire supply that will ever exist.
Two addresses received 92.2 billion coins each. The miner who solved the block collected an extra 0.01 BTC that had never existed before.
The cause was an integer overflow. The code checked that the outputs of a transaction added up correctly, but it never considered what happens when the numbers are so large that the sum wraps around and looks small again.
The entire promise of Bitcoin is that the supply cannot be changed by anyone. For a few hours, that promise was dead.
Then the response came. A patched version of the software was released within five hours.
The chain split into two, and many unpatched nodes kept building on the bad one. The honest chain only overtook it at block 74691, and in that moment the 184 billion coins simply stopped existing.
Bitcoin was trading near $0.07 that day. It closed the year above $0.30.
The person who did it has never been identified.