Blockchain isn’t totally foolproof — there are a few ways that it can be hacked. “If 51% of the network of miners, or of work done by miners, is bribed to alter the ledger, this can result in corruption and incorrectness in the ledger.” Additionally, if one of the nodes of the blockchain network is disabled and it cannot communicate, it may be compromised
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That's not what happens. 51% attack can undo the last blocks and replace them with new blocks, but the blocks still have to be valid. They can't edit the blockchain and transfer someone's bitcoins. Your coins can only be stolen if you received them recently. The more confirmations your coins have, the more expensive it is to steal them. It's not about just owning 51% of power, it's about paying for it to execute the attack. So if you receive $10,000,000 worth of BTC, it's better to wait for 50 confirmations or more, before viewing transaction as final. Although there has never been a documented case of a 51% attack on Bitcoin. But it happened with many altcoins.