Chances of hacking are less, but I wouldn't be surprised if Binance has been hacked. Big exchanges like it are always the target of hackers, and you do fail at one or the other time. They are citing the reason of system upgrades, and I hope that's the only reason. But even in case it has been hacked, I would still use it. Having an impenetrable exchange is just not possible, even if top security experts watch over it.