Doggy? (Woof! woof!).
I assume that you mean 'dodgy' ;-)
An IBAN isjust your usual sort code and account number, preceded by additional information to make it meaningful in any country. So, by providing your IBAN, you're not giving away anything which isn't printed on any cheques you might write. It doesn't directly make the funds in your bank account available to anyone but such information could be used (along with your name and address) to fraudulently set up a direct debit to another account.
Chris