[Pyxl101]

If you have someone's bank account number, you can pretty much take money out of it. By default there is no real authorization process by which the account holder is asked to allow the withdrawal. There is just the assumption that people aren't going to commit fraud, or people who commit fraud will be caught.

I'm not an expert on this, but I believe there are ways to set up business accounts where money can't be taken out in that way, at least not by the standard electronic means. You can also manage accounts in such a way as that there's no money to take out, although that does not necessarily prevent the account from going into the negative. Checking accounts can go into significant negative balances if the bank chooses to allow it.

[HenryBemis]

It is more difficult than you describe it. To set up a monthly payment the bank verifies the request (e.g. if you sign such direct debit for the gym or your electricity bill). Every ebamli I ever used has a page with all these direct debit setups and alerts you when a new one is made to bring your attention to it. These also have limits. And a decent bank would scrutinize the direct debit. A gym or Vodafone will fly easier than a direct debit to VodkaPotatoLimited in Russia or China (no offense) when you live in the UK.

As to prevent the overdraft, just ask the bank to NOT have overdraft capacity on your account(s).

[CodeWriter23]

You can just print a check with the account and routing number.