There are rumors that hackers can access and steal bitcoins from our digital wallets but it's still humor and I've never heard personal experience with regards to this matter. Bitcoin network is supported by Blockchain technology, so it's impossible to be hacked since it's the most secure way of storing our digital assets such as BTC. Moreover, there's no record of a security breach on the bitcoin network before so the only way for hackers is to gain access to your digital wallet. So it is most likely caused by carelessness of the owner.