There are currently three ways to steal Bitcoin. First, hackers infect crypto asset exchange servers with special malware via e-mail, websites and popads and infiltrate devices. This happened with the Binance hack last year.
Second, take apart the Bitcoin hardware wallet and get the seed phrase. This has been practiced by Kraken against Trezor.
Third, hacking into the Bitcoin blockchain network itself through “51 Percent Attack”. This third method is considered expensive, but has the potential to get the largest loot than the other two methods. This third method, according to observers, will cost up to US $ 21 million.
Stealing Bitcoin is not hacking it, so the name is misleading. The first hack is the hack of the exchange, not of Bitcoin itself. The second is at best about hacking Trezor wallet, but definitely not Bitcoin. And the third is finally about Bitcoin, but I still wouldn't call it a hack. Then again, it's almost impossible to do this, and I'm pretty sure an attempt would cost way more that $21 million. It seems that it's even hard to calculate how much money it would take because with Bitcoin it's probably not possible to get enough mining power. The only one who's probably able to pull it off is Bitmain, but this would destroy the company, so we are relatively safe from that. What would be a hack on Bitcoin is quantum computers being able to decrypt everything (if that ever happens), but we're not close to that either.