Your checking or savings bank account cannot be hacked with just the bank account number.
However when someone has your bank account number and routing number to the bank then it makes it a bit easier for a bank account to be hacked.
But hacking a bank account involves more than just needing the checking account number and routing number.
But with the checking account number and routing number people can remove money from your bank account but they also usually need your name to setup the automatic debit.
Like for example you can pay bills online through your bank account and you need to enter your bank account number as well as routing number.
Then the company can debit your bank account.
Someone else may be able to do that but it's unlikely and if it were more possible more criminals would be draining peoples bank accounts.