Of course, wallets can be hacked - you cannot really expect the best on everything, someone will always be smarter than anyone else and easily get their way through.
Easiest way into them is through your wallet login credentials so it is important to triple check its safety and never trust anyone.
Right, there is nothing that has never happened before and I have read some articles on how the development of quantum computers can actually create some easy ways to hacking but whichever way I am sure even the protocol of most of the cryptocurrencies must have changed so as to be able to withstand any of such hacking process.
Security is paramount in this crypto world, and that is the only way we can stay out of the hacker's vices. Always using the latest wallet version and using separate computer/laptop for wallets are few security measurements I am following right now.