Good questions : )
I will explain better in a future post about how IOTA works, but in short, the users verify the transactions themselves thus cutting out the middle man (the miners) using a new method called "the Tangle".
With regards to malicious actors, the transaction is verified by three users and if one is deemed false then the transaction is refused. Tangle technology is also quantum resistant, thus it can not be hacked even by future quantum computers